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bpf: Disallow interpreter fallback for BPF_ADDR_PERCPU insn

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The BPF_MOV64_PERCPU_REG insn requires JIT to emit native code to for
'dst_reg = src_reg + <percpu_base_off>'.

However, the interpreter ignores the 'off' at its ALU64_MOV_X label.
The 'off' indicates the insn is BPF_MOV64_PERCPU_REG insn. Then, when
the interpreter loads memory from the register, it will hit a page
fault.

[    2.545572] BUG: unable to handle page fault for address: ffffffffacaaf034
[    2.546485] #PF: supervisor read access in kernel mode
[    2.547167] #PF: error_code(0x0000) - not-present page
[    2.547850] PGD 134e63067 P4D 134e63067 PUD 134e64063 PMD 10021c063 PTE 800ffffeca550062
[    2.548912] Oops: Oops: 0000 [#1] SMP PTI

Set jit_required as true in order to disallow interpreter fallback in
core.c::__bpf_prog_select_runtime(), if any BPF_ADDR_PERCPU insn is
patched to the prog.

BTW, rename the helper bpf_map_supports_cpu_flags() to
bpf_map_is_percpu_map().

Fixes: 7bdbf74463 ("bpf: add special internal-only MOV instruction to resolve per-CPU addrs")
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/bpf/20260715141122.15783-4-leon.hwang@linux.dev
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Leon Hwang 2026-07-15 22:11:22 +08:00 committed by Kumar Kartikeya Dwivedi
parent 905f716362
commit 7a0855e737
No known key found for this signature in database
GPG Key ID: 472D377B63542F83
2 changed files with 7 additions and 2 deletions
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4
include/linux/bpf.h
View File

@ -4163,7 +4163,7 @@ bpf_prog_update_insn_ptrs(struct bpf_prog *prog, u32 *offsets, void *image)
}
#endif
static inline bool bpf_map_supports_cpu_flags(enum bpf_map_type map_type)
static inline bool bpf_map_is_percpu_map(enum bpf_map_type map_type)
{
switch (map_type) {
case BPF_MAP_TYPE_PERCPU_ARRAY:
@ -4190,7 +4190,7 @@ static inline int bpf_map_check_op_flags(struct bpf_map *map, u64 flags, u64 all
return -EINVAL;
if (flags & (BPF_F_CPU | BPF_F_ALL_CPUS)) {
if (!bpf_map_supports_cpu_flags(map->map_type))
if (!bpf_map_is_percpu_map(map->map_type))
return -EINVAL;
if ((flags & BPF_F_CPU) && (flags & BPF_F_ALL_CPUS))
return -EINVAL;

5
kernel/bpf/fixups.c
View File

@ -2008,6 +2008,9 @@ int bpf_do_misc_fixups(struct bpf_verifier_env *env)
return -EFAULT;
}
if (bpf_map_is_percpu_map(map_ptr->map_type))
prog->jit_required = true;
new_prog = bpf_patch_insn_data(env, i + delta,
insn_buf, cnt);
if (!new_prog)
@ -2112,6 +2115,7 @@ int bpf_do_misc_fixups(struct bpf_verifier_env *env)
* way, it's fine to back out this inlining logic
*/
#ifdef CONFIG_SMP
prog->jit_required = true;
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)&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);
@ -2133,6 +2137,7 @@ int bpf_do_misc_fixups(struct bpf_verifier_env *env)
/* Implement bpf_get_current_task() and bpf_get_current_task_btf() inline. */
if ((insn->imm == BPF_FUNC_get_current_task || insn->imm == BPF_FUNC_get_current_task_btf) &&
bpf_verifier_inlines_helper_call(env, insn->imm)) {
prog->jit_required = true;
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)&current_task);
insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);