From: Alexei Starovoitov <ast@kernel.org>
Date: Thu, 16 Dec 2021 02:38:30 +0000 (-0800)
Subject: bpf: Fix extable fixup offset.
X-Git-Tag: baikal/mips/sdk6.1~6857^2^2~3
X-Git-Url: https://git.baikalelectronics.ru/sdk/?a=commitdiff_plain;h=b0b837a54ba0178e375b67ceeb837f10a230d317;p=kernel.git

bpf: Fix extable fixup offset.

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: 643d483d7b91 ("bpf: Emit explicit NULL pointer checks for PROBE_LDX instructions.")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 726700fabca6d..fa58681db45e4 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1305,7 +1305,7 @@ 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;