linux-kernel - [tip: x86/asm] x86/bpf: Fix BPF percpu accesses

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Message-ID: <174068768313.10177.13465442167535423659.tip-bot2@tip-bot2>
Date: Thu, 27 Feb 2025 20:21:23 -0000
From: "tip-bot2 for Brian Gerst" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Brian Gerst <brgerst@...il.com>, Ingo Molnar <mingo@...nel.org>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Uros Bizjak <ubizjak@...il.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/asm] x86/bpf: Fix BPF percpu accesses

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     18cdd90aba794333f4c6dce39f5c3fe642af5575
Gitweb:        https://git.kernel.org/tip/18cdd90aba794333f4c6dce39f5c3fe642af5575
Author:        Brian Gerst <brgerst@...il.com>
AuthorDate:    Thu, 27 Feb 2025 14:53:02 -05:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Thu, 27 Feb 2025 21:10:03 +01:00

x86/bpf: Fix BPF percpu accesses

Due to this recent commit in the x86 tree:

  9d7de2aa8b41 ("Use relative percpu offsets")

percpu addresses went from positive offsets from the GSBASE to negative
kernel virtual addresses.  The BPF verifier has an optimization for
x86-64 that loads the address of cpu_number into a register, but was only
doing a 32-bit load which truncates negative addresses.

Change it to a 64-bit load so that the address is properly sign-extended.

Fixes: 9d7de2aa8b41 ("Use relative percpu offsets")
Signed-off-by: Brian Gerst <brgerst@...il.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Uros Bizjak <ubizjak@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lore.kernel.org/r/20250227195302.1667654-1-brgerst@gmail.com
---
 kernel/bpf/verifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9971c03..f74263b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -21692,7 +21692,7 @@ patch_map_ops_generic:
 			 * way, it's fine to back out this inlining logic
 			 */
 #ifdef CONFIG_SMP
-			insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number);
+			insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number);
 			insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
 			insn_buf[2] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0);
 			cnt = 3;