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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 1.0.7/27489/Mon Dec 16 10:39:01 2024) 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 >> >> 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