Messages in this thread Patch in this message | | | From | Nadav Amit <> | Subject | [PATCH v2] x86/kprobes: Fix 1 byte conditional jump target | Date | Wed, 8 Feb 2023 07:17:08 +0000 |
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From: Nadav Amit <namit@vmware.com>
Commit 3bc753c06dd0 ("kbuild: treat char as always unsigned") broke kprobes. Setting a probe-point on 1 byte conditional jump can cause the kernel to crash, as the branch target is not sign-extended and instead zero-extended.
In fact, there is no need for any casting of immediate.value since sign extension is already done during its decoding in insn_get_immediate().
Fix by removing the casting of the 1 byte conditional jump target. Future patches can also remove the casting (and sign extension) in other cases in which immediate.value is being used.
Fixes: 3bc753c06dd0 ("kbuild: treat char as always unsigned") Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Suggested-by: Dave Hansen <dave.hansen@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Nadav Amit <namit@vmware.com>
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v1->v2: Removing the casting completely [Dave] --- arch/x86/kernel/kprobes/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c index b36f3c367cb2..695873c0f50b 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -625,7 +625,7 @@ static int prepare_emulation(struct kprobe *p, struct insn *insn) /* 1 byte conditional jump */ p->ainsn.emulate_op = kprobe_emulate_jcc; p->ainsn.jcc.type = opcode & 0xf; - p->ainsn.rel32 = *(char *)insn->immediate.bytes; + p->ainsn.rel32 = insn->immediate.value; break; case 0x0f: opcode = insn->opcode.bytes[1]; -- 2.34.1
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