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 --- 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); } __kprobe_emulate_jmp(p, regs, (match && !invert) || (!match && invert)); }
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
The following commit has been merged into the perf/urgent branch of tip:
Commit-ID: 8924779df820c53875abaeb10c648e9cb75b46d4 Gitweb: https://git.kernel.org/tip/8924779df820c53875abaeb10c648e9cb75b46d4 Author: Nadav Amit namit@vmware.com AuthorDate: Sat, 13 Aug 2022 15:59:43 -07:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Sun, 14 Aug 2022 11:27:17 +02:00
x86/kprobes: Fix JNG/JNLE emulation
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'.
Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Signed-off-by: Nadav Amit namit@vmware.com Signed-off-by: Ingo Molnar mingo@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20220813225943.143767-1-namit@vmware.com --- 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 74167dc..4c3c27b 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); } __kprobe_emulate_jmp(p, regs, (match && !invert) || (!match && invert)); }
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