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.
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.
Metrics
Affected Vendors & Products
Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Thu, 17 Sep 2026 16:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | bpf: Reject load-acquire from pointers requiring fault protection | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-17T16:08:03.996Z
Reserved: 2026-09-11T19:38:34.796Z
Link: CVE-2026-90269
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-17T17:17:23.460
Modified: 2026-09-17T17:17:23.460
Link: CVE-2026-90269
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.