From ae052e3ae09572194d7e574906db7272041577d3 Mon Sep 17 00:00:00 2001
From: Nadav Amit <namit@vmware.com>
Date: Wed, 8 Feb 2023 07:17:08 +0000
Subject: [PATCH] x86/kprobes: Fix 1 byte conditional jump target

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 when the (signed) relative jump offset gets treated as
unsigned.

Fix by replacing the unsigned 'immediate.bytes' (plus a cast) with the
signed 'immediate.value' when assigning to the relative jump offset.

[ dhansen: clarified changelog ]

Fixes: 3bc753c06dd0 ("kbuild: treat char as always unsigned")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Nadav Amit <namit@vmware.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20230208071708.4048-1-namit%40vmware.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 b36f3c367cb24..695873c0f50b5 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];