On Sat, Aug 13, 2022 at 03:59:43PM -0700, Nadav Amit wrote:
From: Nadav Amit namit@vmware.com
When kprobes emulates JNG/JNLE instructions on x86 it uses the wrong condition. For JNG (opcode: 0F 8E), according to Intel SDM, the jump is performed if (ZF == 1 or SF != OF). However the kernel emulation currently uses 'and' instead of 'or'.
As a result, setting a kprobe on JNG/JNLE might cause the kernel to behave incorrectly whenever the kprobe is hit.
Fix by changing the 'and' to 'or'.
Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: Andy Lutomirski luto@kernel.org Cc: stable@vger.kernel.org Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Signed-off-by: Nadav Amit namit@vmware.com
Urgghh..
Acked-by: Peter Zijlstra (Intel) peterz@infradead.org
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 74167dc5f55e..4c3c27b6aea3 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -505,7 +505,7 @@ static void kprobe_emulate_jcc(struct kprobe *p, struct pt_regs *regs) match = ((regs->flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^ ((regs->flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT); if (p->ainsn.jcc.type >= 0xe)
match = match && (regs->flags & X86_EFLAGS_ZF);
match = match || (regs->flags & X86_EFLAGS_ZF);}
2.25.1