/* * User-space Probes (UProbes) for x86 * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * Copyright (C) IBM Corporation, 2008-2011 * Authors: * Srikar Dronamraju * Jim Keniston */ #include #include #include #include #include #include #include #include #include /* Post-execution fixups. */ /* Adjust IP back to vicinity of actual insn */ #define UPROBE_FIX_IP 0x01 /* Adjust the return address of a call insn */ #define UPROBE_FIX_CALL 0x02 /* Instruction will modify TF, don't change it */ #define UPROBE_FIX_SETF 0x04 #define UPROBE_FIX_RIP_SI 0x08 #define UPROBE_FIX_RIP_DI 0x10 #define UPROBE_FIX_RIP_BX 0x20 #define UPROBE_FIX_RIP_MASK \ (UPROBE_FIX_RIP_SI | UPROBE_FIX_RIP_DI | UPROBE_FIX_RIP_BX) #define UPROBE_TRAP_NR UINT_MAX /* Adaptations for mhiramat x86 decoder v14. */ #define OPCODE1(insn) ((insn)->opcode.bytes[0]) #define OPCODE2(insn) ((insn)->opcode.bytes[1]) #define OPCODE3(insn) ((insn)->opcode.bytes[2]) #define MODRM_REG(insn) X86_MODRM_REG((insn)->modrm.value) #define W(row, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf)\ (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) | \ (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) | \ (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) | \ (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf)) \ << (row % 32)) /* * Good-instruction tables for 32-bit apps. This is non-const and volatile * to keep gcc from statically optimizing it out, as variable_test_bit makes * some versions of gcc to think only *(unsigned long*) is used. * * Opcodes we'll probably never support: * 6c-6f - ins,outs. SEGVs if used in userspace * e4-e7 - in,out imm. SEGVs if used in userspace * ec-ef - in,out acc. SEGVs if used in userspace * cc - int3. SIGTRAP if used in userspace * ce - into. Not used in userspace - no kernel support to make it useful. SEGVs * (why we support bound (62) then? it's similar, and similarly unused...) * f1 - int1. SIGTRAP if used in userspace * f4 - hlt. SEGVs if used in userspace * fa - cli. SEGVs if used in userspace * fb - sti. SEGVs if used in userspace * * Opcodes which need some work to be supported: * 07,17,1f - pop es/ss/ds * Normally not used in userspace, but would execute if used. * Can cause GP or stack exception if tries to load wrong segment descriptor. * We hesitate to run them under single step since kernel's handling * of userspace single-stepping (TF flag) is fragile. * We can easily refuse to support push es/cs/ss/ds (06/0e/16/1e) * on the same grounds that they are never used. * cd - int N. * Used by userspace for "int 80" syscall entry. (Other "int N" * cause GP -> SEGV since their IDT gates don't allow calls from CPL 3). * Not supported since kernel's handling of userspace single-stepping * (TF flag) is fragile. * cf - iret. Normally not used in userspace. Doesn't SEGV unless arguments are bad */ #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) static volatile u32 good_insns_32[256 / 32] = { /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ /* ---------------------------------------------- */ W(0x00, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1) | /* 00 */ W(0x10, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) , /* 10 */ W(0x20, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 20 */ W(0x30, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 30 */ W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */ W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */ W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */ W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */ W(0x80, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */ W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */ W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */ W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */ W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */ W(0xd0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */ W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* e0 */ W(0xf0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1) /* f0 */ /* ---------------------------------------------- */ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ }; #else #define good_insns_32 NULL #endif /* Good-instruction tables for 64-bit apps. * * Genuinely invalid opcodes: * 06,07 - formerly push/pop es * 0e - formerly push cs * 16,17 - formerly push/pop ss * 1e,1f - formerly push/pop ds * 27,2f,37,3f - formerly daa/das/aaa/aas * 60,61 - formerly pusha/popa * 62 - formerly bound. EVEX prefix for AVX512 (not yet supported) * 82 - formerly redundant encoding of Group1 * 9a - formerly call seg:ofs * ce - formerly into * d4,d5 - formerly aam/aad * d6 - formerly undocumented salc * ea - formerly jmp seg:ofs * * Opcodes we'll probably never support: * 6c-6f - ins,outs. SEGVs if used in userspace * e4-e7 - in,out imm. SEGVs if used in userspace * ec-ef - in,out acc. SEGVs if used in userspace * cc - int3. SIGTRAP if used in userspace * f1 - int1. SIGTRAP if used in userspace * f4 - hlt. SEGVs if used in userspace * fa - cli. SEGVs if used in userspace * fb - sti. SEGVs if used in userspace * * Opcodes which need some work to be supported: * cd - int N. * Used by userspace for "int 80" syscall entry. (Other "int N" * cause GP -> SEGV since their IDT gates don't allow calls from CPL 3). * Not supported since kernel's handling of userspace single-stepping * (TF flag) is fragile. * cf - iret. Normally not used in userspace. Doesn't SEGV unless arguments are bad */ #if defined(CONFIG_X86_64) static volatile u32 good_insns_64[256 / 32] = { /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ /* ---------------------------------------------- */ W(0x00, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 1) | /* 00 */ W(0x10, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 10 */ W(0x20, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) | /* 20 */ W(0x30, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) , /* 30 */ W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */ W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */ W(0x60, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */ W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */ W(0x80, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */ W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1) , /* 90 */ W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */ W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */ W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */ W(0xd0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */ W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0) | /* e0 */ W(0xf0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1) /* f0 */ /* ---------------------------------------------- */ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ }; #else #define good_insns_64 NULL #endif /* Using this for both 64-bit and 32-bit apps. * Opcodes we don't support: * 0f 00 - SLDT/STR/LLDT/LTR/VERR/VERW/-/- group. System insns * 0f 01 - SGDT/SIDT/LGDT/LIDT/SMSW/-/LMSW/INVLPG group. * Also encodes tons of other system insns if mod=11. * Some are in fact non-system: xend, xtest, rdtscp, maybe more * 0f 05 - syscall * 0f 06 - clts (CPL0 insn) * 0f 07 - sysret * 0f 08 - invd (CPL0 insn) * 0f 09 - wbinvd (CPL0 insn) * 0f 0b - ud2 * 0f 30 - wrmsr (CPL0 insn) (then why rdmsr is allowed, it's also CPL0 insn?) * 0f 34 - sysenter * 0f 35 - sysexit * 0f 37 - getsec * 0f 78 - vmread (Intel VMX. CPL0 insn) * 0f 79 - vmwrite (Intel VMX. CPL0 insn) * Note: with prefixes, these two opcodes are * extrq/insertq/AVX512 convert vector ops. * 0f ae - group15: [f]xsave,[f]xrstor,[v]{ld,st}mxcsr,clflush[opt], * {rd,wr}{fs,gs}base,{s,l,m}fence. * Why? They are all user-executable. */ static volatile u32 good_2byte_insns[256 / 32] = { /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ /* ---------------------------------------------- */ W(0x00, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1) | /* 00 */ W(0x10, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 10 */ W(0x20, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 20 */ W(0x30, 0, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1) , /* 30 */ W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */ W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */ W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 60 */ W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1) , /* 70 */ W(0x80, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */ W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */ W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1) | /* a0 */ W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */ W(0xc0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* c0 */ W(0xd0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */ W(0xe0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* e0 */ W(0xf0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) /* f0 */ /* ---------------------------------------------- */ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ }; #undef W /* * opcodes we may need to refine support for: * * 0f - 2-byte instructions: For many of these instructions, the validity * depends on the prefix and/or the reg field. On such instructions, we * just consider the opcode combination valid if it corresponds to any * valid instruction. * * 8f - Group 1 - only reg = 0 is OK * c6-c7 - Group 11 - only reg = 0 is OK * d9-df - fpu insns with some illegal encodings * f2, f3 - repnz, repz prefixes. These are also the first byte for * certain floating-point instructions, such as addsd. * * fe - Group 4 - only reg = 0 or 1 is OK * ff - Group 5 - only reg = 0-6 is OK * * others -- Do we need to support these? * * 0f - (floating-point?) prefetch instructions * 07, 17, 1f - pop es, pop ss, pop ds * 26, 2e, 36, 3e - es:, cs:, ss:, ds: segment prefixes -- * but 64 and 65 (fs: and gs:) seem to be used, so we support them * 67 - addr16 prefix * ce - into * f0 - lock prefix */ /* * TODO: * - Where necessary, examine the modrm byte and allow only valid instructions * in the different Groups and fpu instructions. */ static bool is_prefix_bad(struct insn *insn) { int i; for (i = 0; i < insn->prefixes.nbytes; i++) { insn_attr_t attr; attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]); switch (attr) { case INAT_MAKE_PREFIX(INAT_PFX_ES): case INAT_MAKE_PREFIX(INAT_PFX_CS): case INAT_MAKE_PREFIX(INAT_PFX_DS): case INAT_MAKE_PREFIX(INAT_PFX_SS): case INAT_MAKE_PREFIX(INAT_PFX_LOCK): return true; } } return false; } static int uprobe_init_insn(struct arch_uprobe *auprobe, struct insn *insn, bool x86_64) { u32 volatile *good_insns; insn_init(insn, auprobe->insn, sizeof(auprobe->insn), x86_64); /* has the side-effect of processing the entire instruction */ insn_get_length(insn); if (!insn_complete(insn)) return -ENOEXEC; if (is_prefix_bad(insn)) return -ENOTSUPP; /* We should not singlestep on the exception masking instructions */ if (insn_masking_exception(insn)) return -ENOTSUPP; if (x86_64) good_insns = good_insns_64; else good_insns = good_insns_32; if (test_bit(OPCODE1(insn), (unsigned long *)good_insns)) return 0; if (insn->opcode.nbytes == 2) { if (test_bit(OPCODE2(insn), (unsigned long *)good_2byte_insns)) return 0; } return -ENOTSUPP; } #ifdef CONFIG_X86_64 /* * If arch_uprobe->insn doesn't use rip-relative addressing, return * immediately. Otherwise, rewrite the instruction so that it accesses * its memory operand indirectly through a scratch register. Set * defparam->fixups accordingly. (The contents of the scratch register * will be saved before we single-step the modified instruction, * and restored afterward). * * We do this because a rip-relative instruction can access only a * relatively small area (+/- 2 GB from the instruction), and the XOL * area typically lies beyond that area. At least for instructions * that store to memory, we can't execute the original instruction * and "fix things up" later, because the misdirected store could be * disastrous. * * Some useful facts about rip-relative instructions: * * - There's always a modrm byte with bit layout "00 reg 101". * - There's never a SIB byte. * - The displacement is always 4 bytes. * - REX.B=1 bit in REX prefix, which normally extends r/m field, * has no effect on rip-relative mode. It doesn't make modrm byte * with r/m=101 refer to register 1101 = R13. */ static void riprel_analyze(struct arch_uprobe *auprobe, struct insn *insn) { u8 *cursor; u8 reg; u8 reg2; if (!insn_rip_relative(insn)) return; /* * insn_rip_relative() would have decoded rex_prefix, vex_prefix, modrm. * Clear REX.b bit (extension of MODRM.rm field): * we want to encode low numbered reg, not r8+. */ if (insn->rex_prefix.nbytes) { cursor = auprobe->insn + insn_offset_rex_prefix(insn); /* REX byte has 0100wrxb layout, clearing REX.b bit */ *cursor &= 0xfe; } /* * Similar treatment for VEX3/EVEX prefix. * TODO: add XOP treatment when insn decoder supports them */ if (insn->vex_prefix.nbytes >= 3) { /* * vex2: c5 rvvvvLpp (has no b bit) * vex3/xop: c4/8f rxbmmmmm wvvvvLpp * evex: 62 rxbR00mm wvvvv1pp zllBVaaa * Setting VEX3.b (setting because it has inverted meaning). * Setting EVEX.x since (in non-SIB encoding) EVEX.x * is the 4th bit of MODRM.rm, and needs the same treatment. * For VEX3-encoded insns, VEX3.x value has no effect in * non-SIB encoding, the change is superfluous but harmless. */ cursor = auprobe->insn + insn_offset_vex_prefix(insn) + 1; *cursor |= 0x60; } /* * Convert from rip-relative addressing to register-relative addressing * via a scratch register. * * This is tricky since there are insns with modrm byte * which also use registers not encoded in modrm byte: * [i]div/[i]mul: implicitly use dx:ax * shift ops: implicitly use cx * cmpxchg: implicitly uses ax * cmpxchg8/16b: implicitly uses dx:ax and bx:cx * Encoding: 0f c7/1 modrm * The code below thinks that reg=1 (cx), chooses si as scratch. * mulx: implicitly uses dx: mulx r/m,r1,r2 does r1:r2 = dx * r/m. * First appeared in Haswell (BMI2 insn). It is vex-encoded. * Example where none of bx,cx,dx can be used as scratch reg: * c4 e2 63 f6 0d disp32 mulx disp32(%rip),%ebx,%ecx * [v]pcmpistri: implicitly uses cx, xmm0 * [v]pcmpistrm: implicitly uses xmm0 * [v]pcmpestri: implicitly uses ax, dx, cx, xmm0 * [v]pcmpestrm: implicitly uses ax, dx, xmm0 * Evil SSE4.2 string comparison ops from hell. * maskmovq/[v]maskmovdqu: implicitly uses (ds:rdi) as destination. * Encoding: 0f f7 modrm, 66 0f f7 modrm, vex-encoded: c5 f9 f7 modrm. * Store op1, byte-masked by op2 msb's in each byte, to (ds:rdi). * AMD says it has no 3-operand form (vex.vvvv must be 1111) * and that it can have only register operands, not mem * (its modrm byte must have mode=11). * If these restrictions will ever be lifted, * we'll need code to prevent selection of di as scratch reg! * * Summary: I don't know any insns with modrm byte which * use SI register implicitly. DI register is used only * by one insn (maskmovq) and BX register is used * only by one too (cmpxchg8b). * BP is stack-segment based (may be a problem?). * AX, DX, CX are off-limits (many implicit users). * SP is unusable (it's stack pointer - think about "pop mem"; * also, rsp+disp32 needs sib encoding -> insn length change). */ reg = MODRM_REG(insn); /* Fetch modrm.reg */ reg2 = 0xff; /* Fetch vex.vvvv */ if (insn->vex_prefix.nbytes) reg2 = insn->vex_prefix.bytes[2]; /* * TODO: add XOP vvvv reading. * * vex.vvvv field is in bits 6-3, bits are inverted. * But in 32-bit mode, high-order bit may be ignored. * Therefore, let's consider only 3 low-order bits. */ reg2 = ((reg2 >> 3) & 0x7) ^ 0x7; /* * Register numbering is ax,cx,dx,bx, sp,bp,si,di, r8..r15. * * Choose scratch reg. Order is important: must not select bx * if we can use si (cmpxchg8b case!) */ if (reg != 6 && reg2 != 6) { reg2 = 6; auprobe->defparam.fixups |= UPROBE_FIX_RIP_SI; } else if (reg != 7 && reg2 != 7) { reg2 = 7; auprobe->defparam.fixups |= UPROBE_FIX_RIP_DI; /* TODO (paranoia): force maskmovq to not use di */ } else { reg2 = 3; auprobe->defparam.fixups |= UPROBE_FIX_RIP_BX; } /* * Point cursor at the modrm byte. The next 4 bytes are the * displacement. Beyond the displacement, for some instructions, * is the immediate operand. */ cursor = auprobe->insn + insn_offset_modrm(insn); /* * Change modrm from "00 reg 101" to "10 reg reg2". Example: * 89 05 disp32 mov %eax,disp32(%rip) becomes * 89 86 disp32 mov %eax,disp32(%rsi) */ *cursor = 0x80 | (reg << 3) | reg2; } static inline unsigned long * scratch_reg(struct arch_uprobe *auprobe, struct pt_regs *regs) { if (auprobe->defparam.fixups & UPROBE_FIX_RIP_SI) return ®s->si; if (auprobe->defparam.fixups & UPROBE_FIX_RIP_DI) return ®s->di; return ®s->bx; } /* * If we're emulating a rip-relative instruction, save the contents * of the scratch register and store the target address in that register. */ static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) { if (auprobe->defparam.fixups & UPROBE_FIX_RIP_MASK) { struct uprobe_task *utask = current->utask; unsigned long *sr = scratch_reg(auprobe, regs); utask->autask.saved_scratch_register = *sr; *sr = utask->vaddr + auprobe->defparam.ilen; } } static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) { if (auprobe->defparam.fixups & UPROBE_FIX_RIP_MASK) { struct uprobe_task *utask = current->utask; unsigned long *sr = scratch_reg(auprobe, regs); *sr = utask->autask.saved_scratch_register; } } #else /* 32-bit: */ /* * No RIP-relative addressing on 32-bit */ static void riprel_analyze(struct arch_uprobe *auprobe, struct insn *insn) { } static void riprel_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) { } static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) { } #endif /* CONFIG_X86_64 */ struct uprobe_xol_ops { bool (*emulate)(struct arch_uprobe *, struct pt_regs *); int (*pre_xol)(struct arch_uprobe *, struct pt_regs *); int (*post_xol)(struct arch_uprobe *, struct pt_regs *); void (*abort)(struct arch_uprobe *, struct pt_regs *); }; static inline int sizeof_long(struct pt_regs *regs) { /* * Check registers for mode as in_xxx_syscall() does not apply here. */ return user_64bit_mode(regs) ? 8 : 4; } static int default_pre_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs) { riprel_pre_xol(auprobe, regs); return 0; } static int emulate_push_stack(struct pt_regs *regs, unsigned long val) { unsigned long new_sp = regs->sp - sizeof_long(regs); if (copy_to_user((void __user *)new_sp, &val, sizeof_long(regs))) return -EFAULT; regs->sp = new_sp; return 0; } /* * We have to fix things up as follows: * * Typically, the new ip is relative to the copied instruction. We need * to make it relative to the original instruction (FIX_IP). Exceptions * are return instructions and absolute or indirect jump or call instructions. * * If the single-stepped instruction was a call, the return address that * is atop the stack is the address following the copied instruction. We * need to make it the address following the original instruction (FIX_CALL). * * If the original instruction was a rip-relative instruction such as * "movl %edx,0xnnnn(%rip)", we have instead executed an equivalent * instruction using a scratch register -- e.g., "movl %edx,0xnnnn(%rsi)". * We need to restore the contents of the scratch register * (FIX_RIP_reg). */ static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs) { struct uprobe_task *utask = current->utask; riprel_post_xol(auprobe, regs); if (auprobe->defparam.fixups & UPROBE_FIX_IP) { long correction = utask->vaddr - utask->xol_vaddr; regs->ip += correction; } else if (auprobe->defparam.fixups & UPROBE_FIX_CALL) { regs->sp += sizeof_long(regs); /* Pop incorrect return address */ if (emulate_push_stack(regs, utask->vaddr + auprobe->defparam.ilen)) return -ERESTART; } /* popf; tell the caller to not touch TF */ if (auprobe->defparam.fixups & UPROBE_FIX_SETF) utask->autask.saved_tf = true; return 0; } static void default_abort_op(struct arch_uprobe *auprobe, struct pt_regs *regs) { riprel_post_xol(auprobe, regs); } static const struct uprobe_xol_ops default_xol_ops = { .pre_xol = default_pre_xol_op, .post_xol = default_post_xol_op, .abort = default_abort_op, }; static bool branch_is_call(struct arch_uprobe *auprobe) { return auprobe->branch.opc1 == 0xe8; } #define CASE_COND \ COND(70, 71, XF(OF)) \ COND(72, 73, XF(CF)) \ COND(74, 75, XF(ZF)) \ COND(78, 79, XF(SF)) \ COND(7a, 7b, XF(PF)) \ COND(76, 77, XF(CF) || XF(ZF)) \ COND(7c, 7d, XF(SF) != XF(OF)) \ COND(7e, 7f, XF(ZF) || XF(SF) != XF(OF)) #define COND(op_y, op_n, expr) \ case 0x ## op_y: DO((expr) != 0) \ case 0x ## op_n: DO((expr) == 0) #define XF(xf) (!!(flags & X86_EFLAGS_ ## xf)) static bool is_cond_jmp_opcode(u8 opcode) { switch (opcode) { #define DO(expr) \ return true; CASE_COND #undef DO default: return false; } } static bool check_jmp_cond(struct arch_uprobe *auprobe, struct pt_regs *regs) { unsigned long flags = regs->flags; switch (auprobe->branch.opc1) { #define DO(expr) \ return expr; CASE_COND #undef DO default: /* not a conditional jmp */ return true; } } #undef XF #undef COND #undef CASE_COND static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs) { unsigned long new_ip = regs->ip += auprobe->branch.ilen; unsigned long offs = (long)auprobe->branch.offs; if (branch_is_call(auprobe)) { /* * If it fails we execute this (mangled, see the comment in * branch_clear_offset) insn out-of-line. In the likely case * this should trigger the trap, and the probed application * should die or restart the same insn after it handles the * signal, arch_uprobe_post_xol() won't be even called. * * But there is corner case, see the comment in ->post_xol(). */ if (emulate_push_stack(regs, new_ip)) return false; } else if (!check_jmp_cond(auprobe, regs)) { offs = 0; } regs->ip = new_ip + offs; return true; } static bool push_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs) { unsigned long *src_ptr = (void *)regs + auprobe->push.reg_offset; if (emulate_push_stack(regs, *src_ptr)) return false; regs->ip += auprobe->push.ilen; return true; } static int branch_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs) { BUG_ON(!branch_is_call(auprobe)); /* * We can only get here if branch_emulate_op() failed to push the ret * address _and_ another thread expanded our stack before the (mangled) * "call" insn was executed out-of-line. Just restore ->sp and restart. * We could also restore ->ip and try to call branch_emulate_op() again. */ regs->sp += sizeof_long(regs); return -ERESTART; } static void branch_clear_offset(struct arch_uprobe *auprobe, struct insn *insn) { /* * Turn this insn into "call 1f; 1:", this is what we will execute * out-of-line if ->emulate() fails. We only need this to generate * a trap, so that the probed task receives the correct signal with * the properly filled siginfo. * * But see the comment in ->post_xol(), in the unlikely case it can * succeed. So we need to ensure that the new ->ip can not fall into * the non-canonical area and trigger #GP. * * We could turn it into (say) "pushf", but then we would need to * divorce ->insn[] and ->ixol[]. We need to preserve the 1st byte * of ->insn[] for set_orig_insn(). */ memset(auprobe->insn + insn_offset_immediate(insn), 0, insn->immediate.nbytes); } static const struct uprobe_xol_ops branch_xol_ops = { .emulate = branch_emulate_op, .post_xol = branch_post_xol_op, }; static const struct uprobe_xol_ops push_xol_ops = { .emulate = push_emulate_op, }; /* Returns -ENOSYS if branch_xol_ops doesn't handle this insn */ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn) { u8 opc1 = OPCODE1(insn); int i; switch (opc1) { case 0xeb: /* jmp 8 */ case 0xe9: /* jmp 32 */ case 0x90: /* prefix* + nop; same as jmp with .offs = 0 */ break; case 0xe8: /* call relative */ branch_clear_offset(auprobe, insn); break; case 0x0f: if (insn->opcode.nbytes != 2) return -ENOSYS; /* * If it is a "near" conditional jmp, OPCODE2() - 0x10 matches * OPCODE1() of the "short" jmp which checks the same condition. */ opc1 = OPCODE2(insn) - 0x10; default: if (!is_cond_jmp_opcode(opc1)) return -ENOSYS; } /* * 16-bit overrides such as CALLW (66 e8 nn nn) are not supported. * Intel and AMD behavior differ in 64-bit mode: Intel ignores 66 prefix. * No one uses these insns, reject any branch insns with such prefix. */ for (i = 0; i < insn->prefixes.nbytes; i++) { if (insn->prefixes.bytes[i] == 0x66) return -ENOTSUPP; } auprobe->branch.opc1 = opc1; auprobe->branch.ilen = insn->length; auprobe->branch.offs = insn->immediate.value; auprobe->ops = &branch_xol_ops; return 0; } /* Returns -ENOSYS if push_xol_ops doesn't handle this insn */ static int push_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn) { u8 opc1 = OPCODE1(insn), reg_offset = 0; if (opc1 < 0x50 || opc1 > 0x57) return -ENOSYS; if (insn->length > 2) return -ENOSYS; if (insn->length == 2) { /* only support rex_prefix 0x41 (x64 only) */ #ifdef CONFIG_X86_64 if (insn->rex_prefix.nbytes != 1 || insn->rex_prefix.bytes[0] != 0x41) return -ENOSYS; switch (opc1) { case 0x50: reg_offset = offsetof(struct pt_regs, r8); break; case 0x51: reg_offset = offsetof(struct pt_regs, r9); break; case 0x52: reg_offset = offsetof(struct pt_regs, r10); break; case 0x53: reg_offset = offsetof(struct pt_regs, r11); break; case 0x54: reg_offset = offsetof(struct pt_regs, r12); break; case 0x55: reg_offset = offsetof(struct pt_regs, r13); break; case 0x56: reg_offset = offsetof(struct pt_regs, r14); break; case 0x57: reg_offset = offsetof(struct pt_regs, r15); break; } #else return -ENOSYS; #endif } else { switch (opc1) { case 0x50: reg_offset = offsetof(struct pt_regs, ax); break; case 0x51: reg_offset = offsetof(struct pt_regs, cx); break; case 0x52: reg_offset = offsetof(struct pt_regs, dx); break; case 0x53: reg_offset = offsetof(struct pt_regs, bx); break; case 0x54: reg_offset = offsetof(struct pt_regs, sp); break; case 0x55: reg_offset = offsetof(struct pt_regs, bp); break; case 0x56: reg_offset = offsetof(struct pt_regs, si); break; case 0x57: reg_offset = offsetof(struct pt_regs, di); break; } } auprobe->push.reg_offset = reg_offset; auprobe->push.ilen = insn->length; auprobe->ops = &push_xol_ops; return 0; } /** * arch_uprobe_analyze_insn - instruction analysis including validity and fixups. * @mm: the probed address space. * @arch_uprobe: the probepoint information. * @addr: virtual address at which to install the probepoint * Return 0 on success or a -ve number on error. */ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long addr) { struct insn insn; u8 fix_ip_or_call = UPROBE_FIX_IP; int ret; ret = uprobe_init_insn(auprobe, &insn, is_64bit_mm(mm)); if (ret) return ret; ret = branch_setup_xol_ops(auprobe, &insn); if (ret != -ENOSYS) return ret; ret = push_setup_xol_ops(auprobe, &insn); if (ret != -ENOSYS) return ret; /* * Figure out which fixups default_post_xol_op() will need to perform, * and annotate defparam->fixups accordingly. */ switch (OPCODE1(&insn)) { case 0x9d: /* popf */ auprobe->defparam.fixups |= UPROBE_FIX_SETF; break; case 0xc3: /* ret or lret -- ip is correct */ case 0xcb: case 0xc2: case 0xca: case 0xea: /* jmp absolute -- ip is correct */ fix_ip_or_call = 0; break; case 0x9a: /* call absolute - Fix return addr, not ip */ fix_ip_or_call = UPROBE_FIX_CALL; break; case 0xff: switch (MODRM_REG(&insn)) { case 2: case 3: /* call or lcall, indirect */ fix_ip_or_call = UPROBE_FIX_CALL; break; case 4: case 5: /* jmp or ljmp, indirect */ fix_ip_or_call = 0; break; } /* fall through */ default: riprel_analyze(auprobe, &insn); } auprobe->defparam.ilen = insn.length; auprobe->defparam.fixups |= fix_ip_or_call; auprobe->ops = &default_xol_ops; return 0; } /* * arch_uprobe_pre_xol - prepare to execute out of line. * @auprobe: the probepoint information. * @regs: reflects the saved user state of current task. */ int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) { struct uprobe_task *utask = current->utask; if (auprobe->ops->pre_xol) { int err = auprobe->ops->pre_xol(auprobe, regs); if (err) return err; } regs->ip = utask->xol_vaddr; utask->autask.saved_trap_nr = current->thread.trap_nr; current->thread.trap_nr = UPROBE_TRAP_NR; utask->autask.saved_tf = !!(regs->flags & X86_EFLAGS_TF); regs->flags |= X86_EFLAGS_TF; if (test_tsk_thread_flag(current, TIF_BLOCKSTEP)) set_task_blockstep(current, false); return 0; } /* * If xol insn itself traps and generates a signal(Say, * SIGILL/SIGSEGV/etc), then detect the case where a singlestepped * instruction jumps back to its own address. It is assumed that anything * like do_page_fault/do_trap/etc sets thread.trap_nr != -1. * * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr, * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to * UPROBE_TRAP_NR == -1 set by arch_uprobe_pre_xol(). */ bool arch_uprobe_xol_was_trapped(struct task_struct *t) { if (t->thread.trap_nr != UPROBE_TRAP_NR) return true; return false; } /* * Called after single-stepping. To avoid the SMP problems that can * occur when we temporarily put back the original opcode to * single-step, we single-stepped a copy of the instruction. * * This function prepares to resume execution after the single-step. */ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) { struct uprobe_task *utask = current->utask; bool send_sigtrap = utask->autask.saved_tf; int err = 0; WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR); current->thread.trap_nr = utask->autask.saved_trap_nr; if (auprobe->ops->post_xol) { err = auprobe->ops->post_xol(auprobe, regs); if (err) { /* * Restore ->ip for restart or post mortem analysis. * ->post_xol() must not return -ERESTART unless this * is really possible. */ regs->ip = utask->vaddr; if (err == -ERESTART) err = 0; send_sigtrap = false; } } /* * arch_uprobe_pre_xol() doesn't save the state of TIF_BLOCKSTEP * so we can get an extra SIGTRAP if we do not clear TF. We need * to examine the opcode to make it right. */ if (send_sigtrap) send_sig(SIGTRAP, current, 0); if (!utask->autask.saved_tf) regs->flags &= ~X86_EFLAGS_TF; return err; } /* callback routine for handling exceptions. */ int arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val, void *data) { struct die_args *args = data; struct pt_regs *regs = args->regs; int ret = NOTIFY_DONE; /* We are only interested in userspace traps */ if (regs && !user_mode(regs)) return NOTIFY_DONE; switch (val) { case DIE_INT3: if (uprobe_pre_sstep_notifier(regs)) ret = NOTIFY_STOP; break; case DIE_DEBUG: if (uprobe_post_sstep_notifier(regs)) ret = NOTIFY_STOP; default: break; } return ret; } /* * This function gets called when XOL instruction either gets trapped or * the thread has a fatal signal. Reset the instruction pointer to its * probed address for the potential restart or for post mortem analysis. */ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) { struct uprobe_task *utask = current->utask; if (auprobe->ops->abort) auprobe->ops->abort(auprobe, regs); current->thread.trap_nr = utask->autask.saved_trap_nr; regs->ip = utask->vaddr; /* clear TF if it was set by us in arch_uprobe_pre_xol() */ if (!utask->autask.saved_tf) regs->flags &= ~X86_EFLAGS_TF; } static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs) { if (auprobe->ops->emulate) return auprobe->ops->emulate(auprobe, regs); return false; } bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs) { bool ret = __skip_sstep(auprobe, regs); if (ret && (regs->flags & X86_EFLAGS_TF)) send_sig(SIGTRAP, current, 0); return ret; } unsigned long arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs) { int rasize = sizeof_long(regs), nleft; unsigned long orig_ret_vaddr = 0; /* clear high bits for 32-bit apps */ if (copy_from_user(&orig_ret_vaddr, (void __user *)regs->sp, rasize)) return -1; /* check whether address has been already hijacked */ if (orig_ret_vaddr == trampoline_vaddr) return orig_ret_vaddr; nleft = copy_to_user((void __user *)regs->sp, &trampoline_vaddr, rasize); if (likely(!nleft)) return orig_ret_vaddr; if (nleft != rasize) { pr_err("return address clobbered: pid=%d, %%sp=%#lx, %%ip=%#lx\n", current->pid, regs->sp, regs->ip); force_sig_info(SIGSEGV, SEND_SIG_FORCED, current); } return -1; } bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx, struct pt_regs *regs) { if (ctx == RP_CHECK_CALL) /* sp was just decremented by "call" insn */ return regs->sp < ret->stack; else return regs->sp <= ret->stack; }