linux-kernel - [PATCH 5.15 110/177] bpf: Fix extable fixup offset.

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Date:   Mon, 20 Dec 2021 15:34:20 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 110/177] bpf: Fix extable fixup offset.

From: Alexei Starovoitov <ast@...nel.org>

[ Upstream commit 433956e91200734d09958673a56df02d00a917c2 ]

The prog - start_of_ldx is the offset before the faulting ldx to the location
after it, so this will be used to adjust pt_regs->ip for jumping over it and
continuing, and with old temp it would have been fixed up to the wrong offset,
causing crash.

Fixes: 4c5de127598e ("bpf: Emit explicit NULL pointer checks for PROBE_LDX instructions.")
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Reviewed-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/net/bpf_jit_comp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 9ea57389c554b..462d8e68b3f43 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1332,7 +1332,7 @@ st:			if (is_imm8(insn->off))
 				 * End result: x86 insn "mov rbx, qword ptr [rax+0x14]"
 				 * of 4 bytes will be ignored and rbx will be zero inited.
 				 */
-				ex->fixup = (prog - temp) | (reg2pt_regs[dst_reg] << 8);
+				ex->fixup = (prog - start_of_ldx) | (reg2pt_regs[dst_reg] << 8);
 			}
 			break;
 
-- 
2.33.0