x86/kprobes: Fix JNG/JNLE emulation

BugLink: https://bugs.launchpad.net/bugs/1990564
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@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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 7a7f671c60b4a500c6f47d42236d983bbcf549bc..6872f3834668da3356cdc78eb883634285e343c7 100644 (file)
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -495,7 +495,7 @@ 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));
 }