CVE-2026-90269

In the Linux kernel, the following vulnerability has been resolved:

bpf: Reject load-acquire from pointers requiring fault protection

A BPF_LOAD_ACQ is not rewritten to a BPF_PROBE_MEM load by the verifier,

unlike a regular BPF_LDX, so the JIT emits a plain load with no exception

table entry and a fault panics the kernel instead of being handled.

Reject the source pointer types that a BPF_LDX would have had that fault

protection applied to, i.e. the ones bpf_convert_ctx_accesses() turns

into BPF_PROBE_MEM: a bare PTR_TO_BTF_ID, PTR_TO_BTF_ID | PTR_UNTRUSTED,

PTR_TO_BTF_ID | MEM_ALLOC | PTR_UNTRUSTED and PTR_TO_MEM | MEM_RDONLY |

PTR_UNTRUSTED.

This is reachable e.g. by loading ->mm out of a trusted task_struct

yields an untrusted pointer to mm_struct, and it is NULL for a kernel

thread:

[...]

SEC("tp_btf/sched_switch")

int BPF_PROG(demo, bool preempt, struct task_struct *prev,

struct task_struct *next)

{

struct mm_struct *mm = next->mm; /* untrusted */

out_ldx = (__u64)mm->pgd; /* BPF_LDX */

out_acq = load_acquire(&mm->pgd); /* BPF_LOAD_ACQ */

return 0;

}

[...]

Both dereference the same pointer, but only the BPF_LDX is protected

(x86-64 JIT, jump targets shown prog-relative):

[...]

; out_ldx = (__u64)mm->pgd;

17: movq $-10485760, %r10

1e: movq %rsi, %r11

21: addq $184, %r11

28: subq %r10, %r11

2b: movabsq $140737498841088, %r10

35: cmpq %r10, %r11

38: ja 0x3e <-- kernel addr?

3a: xorl %edi, %edi <-- no: dst = 0, skip the load

3c: jmp 0x45

3e: movq 184(%rsi), %rdi <-- yes: load + extable entry

[...]

; load_acquire(&mm->pgd)

53: movq %rsi, %rdi

56: movq 184(%rdi), %rax <-- no check, no extable entry

[...]

Note that BPF_PROBE_MEM is not visible in a bpftool xlated dump, as

bpf_insn_prepare_dump() rewrites it back to BPF_MEM.

A PTR_TRUSTED pointer is deliberately not on the list. Such a load is

not converted either, but it does not need to be, since the pointer is

guaranteed live, so load-acquire from it stays allowed.

The check is gated on BPF_LOAD_ACQ so that atomic RMW and store-release

error messages are unchanged; writes (RMW / store-release) to such

pointers are already rejected elsewhere, so only load-acquire needs this.