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bpf: Fix bpf_get_smp_processor_id() on !CONFIG_SMP

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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: 1ae6921009 ("bpf: inline bpf_get_smp_processor_id() helper")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241217195813.622568-1-arighi@nvidia.com
This commit is contained in:
Andrea Righi 2024-12-17 20:58:13 +01:00 committed by Andrii Nakryiko
parent 78d4f34e21
commit 23579010cf
1 changed files with 5 additions and 1 deletions
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6
kernel/bpf/verifier.c
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@ -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;