Re: [PATCH] bpf: do not inline bpf_get_smp_processor_id() with CONFIG_SMP disabled
From: Daniel Borkmann
Date: Mon Dec 16 2024 - 15:28:59 EST
On 12/16/24 6:24 PM, Andrea Righi wrote:
On Mon, Dec 16, 2024 at 05:16:33PM +0100, Daniel Borkmann wrote:
On 12/16/24 11:46 AM, Andrea Righi wrote:
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 preventing the inlining of bpf_get_smp_processor_id() when
CONFIG_SMP disabled.
Fixes: 1ae6921009e5 ("bpf: inline bpf_get_smp_processor_id() helper")
Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
lgtm, but can't we instead do sth like this :
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f7f892a52a37..761c70899754 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
+ 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;
That works as well (just tested) and it's probably better since we're
basically inlining the return 0. Do you want me to send a v2 with this?
Yes, pls send v2, I think this is better than explicitly calling the
helper under !CONFIG_SMP.
Thanks,
Daniel