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| author | Jon Medhurst <tixy@yxit.co.uk> | 2011-04-08 15:32:55 +0100 |
|---|---|---|
| committer | Nicolas Pitre <nicolas.pitre@linaro.org> | 2011-04-28 23:40:57 -0400 |
| commit | 54823accfcfc715e9e757a621afb40dabc01d033 (patch) | |
| tree | 17707c238fbb07f26769b974bec731945015696e /arch | |
| parent | 6823fc85fcfba11675f2027aadf2d5291c6f351b (diff) | |
| download | linux-54823accfcfc715e9e757a621afb40dabc01d033.tar.gz linux-54823accfcfc715e9e757a621afb40dabc01d033.tar.bz2 linux-54823accfcfc715e9e757a621afb40dabc01d033.zip | |
ARM: kprobes: Reject probing of LDR/STR instructions which update PC unpredictably
Using PC as an base register with writeback is UNPREDICTABLE, as is non
word-sized loads or stores of PC. (We only really care about preventing
loads to PC but it keeps the code simpler if we also exclude stores.)
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm/kernel/kprobes-decode.c | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c index 348ff47acd06..a4dba1f7c87b 100644 --- a/arch/arm/kernel/kprobes-decode.c +++ b/arch/arm/kernel/kprobes-decode.c @@ -70,6 +70,12 @@ #define is_r15(insn, bitpos) (((insn) & (0xf << bitpos)) == (0xf << bitpos)) +/* + * Test if load/store instructions writeback the address register. + * if P (bit 24) == 0 or W (bit 21) == 1 + */ +#define is_writeback(insn) ((insn ^ 0x01000000) & 0x01200000) + #define PSR_fs (PSR_f|PSR_s) #define KPROBE_RETURN_INSTRUCTION 0xe1a0f00e /* mov pc, lr */ @@ -886,6 +892,9 @@ prep_emulate_ldr_str(kprobe_opcode_t insn, struct arch_specific_insn *asi) int not_imm = (insn & (1 << 26)) ? (insn & (1 << 25)) : (~insn & (1 << 22)); + if (is_writeback(insn) && is_r15(insn, 16)) + return INSN_REJECTED; /* Writeback to PC */ + insn &= 0xfff00fff; insn |= 0x00001000; /* Rn = r0, Rd = r1 */ if (not_imm) { @@ -1167,6 +1176,11 @@ space_cccc_000x(kprobe_opcode_t insn, struct arch_specific_insn *asi) } else if ((insn & 0x0e1000d0) == 0x00000d0) { /* STRD/LDRD */ + if ((insn & 0x0000e000) == 0x0000e000) + return INSN_REJECTED; /* Rd is LR or PC */ + if (is_writeback(insn) && is_r15(insn, 16)) + return INSN_REJECTED; /* Writeback to PC */ + insn &= 0xfff00fff; insn |= 0x00002000; /* Rn = r0, Rd = r2 */ if (insn & (1 << 22)) { @@ -1180,6 +1194,9 @@ space_cccc_000x(kprobe_opcode_t insn, struct arch_specific_insn *asi) return INSN_GOOD; } + /* LDRH/STRH/LDRSB/LDRSH */ + if (is_r15(insn, 12)) + return INSN_REJECTED; /* Rd is PC */ return prep_emulate_ldr_str(insn, asi); } |