diff mbox series

[v2] bpf: Fix bpf_get_smp_processor_id() on !CONFIG_SMP

Message ID 20241217195813.622568-1-arighi@nvidia.com (mailing list archive)
State Accepted
Commit 23579010cf0a12476e96a5f1acdf78a9c5843657
Delegated to: BPF
Headers show
Series [v2] bpf: Fix bpf_get_smp_processor_id() on !CONFIG_SMP | expand

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Commit Message

Andrea Righi Dec. 17, 2024, 7:58 p.m. UTC 
On x86-64 calling bpf_get_smp_processor_id() in a kernel with CONFIG_SMP
disabled can trigger the following bug, as pcpu_hot is unavailable:

 [    8.471774] BUG: unable to handle page fault for address: 00000000936a290c
 [    8.471849] #PF: supervisor read access in kernel mode
 [    8.471881] #PF: error_code(0x0000) - not-present page

Fix by inlining a return 0 in the !CONFIG_SMP case.

Fixes: 1ae6921009e5 ("bpf: inline bpf_get_smp_processor_id() helper")
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
 kernel/bpf/verifier.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

ChangeLog v1 -> v2:
 - generate the proper inline code for the !CONFIG_SMP case (this time
   tested with the right .config)

Comments

patchwork-bot+netdevbpf@kernel.org Dec. 18, 2024, 12:20 a.m. UTC | #1 
Hello:

This patch was applied to bpf/bpf.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Tue, 17 Dec 2024 20:58:13 +0100 you wrote:
> On x86-64 calling bpf_get_smp_processor_id() in a kernel with CONFIG_SMP
> disabled can trigger the following bug, as pcpu_hot is unavailable:
> 
>  [    8.471774] BUG: unable to handle page fault for address: 00000000936a290c
>  [    8.471849] #PF: supervisor read access in kernel mode
>  [    8.471881] #PF: error_code(0x0000) - not-present page
> 
> [...]

Here is the summary with links:
  - [v2] bpf: Fix bpf_get_smp_processor_id() on !CONFIG_SMP
    https://git.kernel.org/bpf/bpf/c/23579010cf0a

You are awesome, thank you!
Daniel Borkmann Dec. 18, 2024, 12:22 p.m. UTC | #2 
On 12/17/24 8:58 PM, Andrea Righi wrote:
> On x86-64 calling bpf_get_smp_processor_id() in a kernel with CONFIG_SMP
> disabled can trigger the following bug, as pcpu_hot is unavailable:
> 
>   [    8.471774] BUG: unable to handle page fault for address: 00000000936a290c
>   [    8.471849] #PF: supervisor read access in kernel mode
>   [    8.471881] #PF: error_code(0x0000) - not-present page
> 
> Fix by inlining a return 0 in the !CONFIG_SMP case.
> 
> Fixes: 1ae6921009e5 ("bpf: inline bpf_get_smp_processor_id() helper")
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Signed-off-by: Andrea Righi <arighi@nvidia.com>

Acked-by: Daniel Borkmann <daniel@iogearbox.net>
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f7f892a52a37..77f56674aaa9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -21281,11 +21281,15 @@  static int do_misc_fixups(struct bpf_verifier_env *env)
 			 * changed in some incompatible and hard to support
 			 * 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[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;
-
+#else
+			insn_buf[0] = BPF_ALU32_REG(BPF_XOR, BPF_REG_0, BPF_REG_0);
+			cnt = 1;
+#endif
 			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
 			if (!new_prog)
 				return -ENOMEM;