linux-kernel - [PATCH 1/2] x86/bpf: Fix IP after emitting call depth accounting

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Message-ID: <20240316232104.368561-2-joanbrugueram@gmail.com>
Date: Sat, 16 Mar 2024 23:21:03 +0000
From: Joan Bruguera Micó <joanbrugueram@...il.com>
To: x86@...nel.org,
	linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Uros Bizjak <ubizjak@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Joan Bruguera Micó <joanbrugueram@...il.com>
Subject: [PATCH 1/2] x86/bpf: 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 Micó <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 a7ba8e178645..09f7dc9d4d65 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -479,9 +479,10 @@ 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 = 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)
-- 
2.44.0