Linux Kernel BPF: REG INVARIANTS Violation in Speculative Pointer Arithmetic
CVE-2026-98151 Published on September 25, 2026
bpf: Fix REG INVARIANTS VIOLATION on speculative pointer arithmetic
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix REG INVARIANTS VIOLATION on speculative pointer arithmetic
Take the following unprivileged program as an example:
r0 = bpf_map_lookup_elem(...) /* PTR_TO_MAP_VALUE, offset 0 */
...
14: r0 += r1 /* r1 is a bounded scalar */
15: r9 = r0
Loading it triggers a verifier warning from reg_bounds_sanity_check():
verifier bug: REG INVARIANTS VIOLATION (alu): const subreg tnum out
of sync with range bounds r64={.base=0x0, .size=0x0}
r32={.base=0x0, .size=0xffffffff} var_off=(0x0, 0x0)
What happens:
1. Processing insn 14 (r0 += r1) in adjust_ptr_min_max_vals(), the new
offset is computed into dst_reg's var_off and 32/64-bit ranges.
2. Because pointer registers do not track 32-bit subregister bounds,
__mark_reg32_unbounded() first sets r32 to the full range; r32 is
re-derived from the offset at the end of the function by
reg_bounds_sync().
3. On the unprivileged path, sanitize_ptr_alu() is called and, via
sanitize_speculative_path() -> push_stack(), snapshots the current
register state and schedules the next instruction (insn 15) to be
verified directly as a speculative path.
4. That snapshot is taken between step 2 and the final reg_bounds_sync():
at this point dst_reg's var_off still holds the (const) original
offset while r32 has just been blanked to the full range, i.e. the two
are out of sync. When the speculative path later verifies insn 15
(r9 = r0), the inconsistent state reaches reg_bounds_sanity_check() and
trips the warning.
var_off and the 32-bit range must always be consistent. There are two
ways to keep the snapshot consistent:
1. sync var_off and r32 before the snapshot so they match, or
2. leave r32 at its original (already consistent) value and blank it
only after the snapshot.
The whole point of sanitize_ptr_alu() is to insert a harmless masking
sequence that keeps the access in bounds under speculation, so the state
it snapshots should faithfully represent that. Take approach 2: move
__mark_reg32_unbounded() to after sanitize_ptr_alu(), so the speculative
snapshot keeps the pointer's original, consistent r32. The non-speculative
path is unchanged: r32 is still blanked before the offset is applied and
re-derived by reg_bounds_sync().
Products Associated with CVE-2026-98151
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Affected Versions
Linux:- Version 5f99f312bd3bedb3b266b0d26376a8c500cdc97f and below 21a681526c715aebb4f918b8c131583442d1b3d8 is affected.
- Version 5f99f312bd3bedb3b266b0d26376a8c500cdc97f and below d623a4a58bb238443505d5c2949d1182dcfc26b6 is affected.
- Version 5f99f312bd3bedb3b266b0d26376a8c500cdc97f and below 9f9477ae73de9c5a28e8ab7000d8097b078faee4 is affected.
- Version 5f99f312bd3bedb3b266b0d26376a8c500cdc97f and below 150aeba624e8b7cac51c39440d7e8e1fd11de9a0 is affected.
- Version 6.8 is affected.
- Before 6.8 is unaffected.
- Version 6.12.111, <= 6.12.* is unaffected.
- Version 6.18.53, <= 6.18.* is unaffected.
- Version 7.2.7, <= 7.2.* is unaffected.
- Version 7.3-rc2, <= * is unaffected.