linux-kernel - [PATCH] bpf, x86: Fix IP after emitting call depth accounting

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Date:   Sat,  7 Jan 2023 05:14:56 +0000
From:   Joan Bruguera <joanbrugueram@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc:     "Joan Bruguera" <joanbrugueram@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] bpf, x86: Fix IP after emitting call depth accounting

Adjust the IP passed to `emit_patch` so it calculates the correct offset
for the CALL instruction if `x86_call_depth_emit_accounting` emits code.
Otherwise we will skip some instructions and most likely crash.

Fixes: b2e9dfe54be4 ("x86/bpf: Emit call depth accounting if required")
Link: https://lore.kernel.org/lkml/20230105214922.250473-1-joanbrugueram@gmail.com/
Signed-off-by: Joan Bruguera <joanbrugueram@...il.com>
---
 arch/x86/net/bpf_jit_comp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index b808be77635e..6e696c6b7018 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -343,9 +343,10 @@ static int emit_call(u8 **pprog, void *func, void *ip)
 
 static int emit_rsb_call(u8 **pprog, void *func, void *ip)
 {
+	void *adjusted_ip;
 	OPTIMIZER_HIDE_VAR(func);
-	x86_call_depth_emit_accounting(pprog, func);
-	return emit_patch(pprog, func, ip, 0xE8);
+	adjusted_ip = (u8 *)ip + x86_call_depth_emit_accounting(pprog, func);
+	return emit_patch(pprog, func, adjusted_ip, 0xE8);
 }
 
 static int emit_jump(u8 **pprog, void *func, void *ip)
-- 
2.39.0