linux-kernel - [PATCH] x86 bpf: Fix extable offset calculation

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Date:   Tue, 22 Jun 2021 16:30:26 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     ast@...nel.org
Cc:     ravi.bangoria@...ux.ibm.com, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, daniel@...earbox.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, naveen.n.rao@...ux.vnet.ibm.com
Subject: [PATCH] x86 bpf: Fix extable offset calculation

commit 4c5de127598e1 ("bpf: Emit explicit NULL pointer checks
for PROBE_LDX instructions.") is emitting couple of instructions
before actual load. Consider those additional instructions while
calculating extable offset.

Fixes: 4c5de127598e1 ("bpf: Emit explicit NULL pointer checks for PROBE_LDX instructions.")
Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
---
 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 2a2e290fa5d8..231a8178cc11 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1297,7 +1297,7 @@ st:			if (is_imm8(insn->off))
 			emit_ldx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off);
 			if (BPF_MODE(insn->code) == BPF_PROBE_MEM) {
 				struct exception_table_entry *ex;
-				u8 *_insn = image + proglen;
+				u8 *_insn = image + proglen + (u8)(start_of_ldx - temp);
 				s64 delta;
 
 				/* populate jmp_offset for JMP above */
-- 
2.30.2