linux-kernel - [PATCH 5.15 018/244] x86/kprobes: Fix JNG/JNLE emulation

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Date:   Tue, 23 Aug 2022 10:22:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nadav Amit <namit@...are.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 5.15 018/244] x86/kprobes: Fix JNG/JNLE emulation

From: Nadav Amit <namit@...are.com>

commit 8924779df820c53875abaeb10c648e9cb75b46d4 upstream.

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@...are.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20220813225943.143767-1-namit@vmware.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/kprobes/core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -495,7 +495,7 @@ static void kprobe_emulate_jcc(struct kp
 		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));
 }