bpf: Fix extable fixup offset.

[ 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@kernel.org>
Reviewed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 9ea5738..462d8e6 100644 (file)
--- 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;