In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix pointer-leak due to insufficient speculative store bypass mitigation
To mitigate Spectre v4, 2039f26f3aca ("bpf: Fix leakage due to
insufficient speculative store bypass mitigation") inserts lfence
instructions after 1) initializing a stack slot and 2) spilling a
pointer to the stack.
However, this does not cover cases where a stack slot is first
initialized with a pointer (subject to sanitization) but then
overwritten with a scalar (not subject to sanitization because
the slot was already initialized). In this case, the second write
may be subject to speculative store bypass (SSB) creating a
speculative pointer-as-scalar type confusion. This allows the
program to subsequently leak the numerical pointer value using,
for example, a branch-based cache side channel.
To fix this, also sanitize scalars if they write a stack slot
that previously contained a pointer. Assuming that pointer-spills
are only generated by LLVM on register-pressure, the performance
impact on most real-world BPF programs should be small.
The following unprivileged BPF bytecode drafts a minimal exploit
and the mitigation:
[...]
// r6 = 0 or 1 (skalar, unknown user input)
// r7 = accessible ptr for side channel
// r10 = frame pointer (fp), to be leaked
//
r9 = r10 # fp alias to encourage ssb
*(u64 *)(r9 - 8) = r10 // fp[-8] = ptr, to be leaked
// lfence added here because of pointer spill to stack.
//
// Ommitted: Dummy bpf_ringbuf_output() here to train alias predictor
// for no r9-r10 dependency.
//
*(u64 *)(r10 - 8) = r6 // fp[-8] = scalar, overwrites ptr
// 2039f26f3aca: no lfence added because stack slot was not STACK_INVALID,
// store may be subject to SSB
//
// fix: also add an lfence when the slot contained a ptr
//
r8 = *(u64 *)(r9 - 8)
// r8 = architecturally a scalar, speculatively a ptr
//
// leak ptr using branch-based cache side channel:
r8 &= 1 // choose bit to leak
if r8 == 0 goto SLOW // no mispredict
// architecturally dead code if input r6 is 0,
// only executes speculatively iff ptr bit is 1
r8 = *(u64 *)(r7 + 0) # encode bit in cache (0: slow, 1: fast)
SLOW:
[...]
After running this, the program can time the access to *(r7 + 0) to
determine whether the chosen pointer bit was 0 or 1. Repeat this 64
times to recover the whole address on amd64.
In summary, sanitization can only be skipped if one scalar is
overwritten with another scalar. Scalar-confusion due to speculative
store bypass can not lead to invalid accesses because the pointer
bounds deducted during verification are enforced using branchless
logic. See 979d63d50c0c ("bpf: prevent out of bounds speculation on
pointer arithmetic") for details.
Do not make the mitigation depend on !env->allow_{uninit_stack,ptr_leaks}
because speculative leaks are likely unexpected if these were enabled.
For example, leaking the address to a protected log file may be acceptable
while disabling the mitigation might unintentionally leak the address
into the cached-state of a map that is accessible to unprivileged
processes.
References
Configurations
Configuration 1 (hide)
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History
22 Jan 2026, 20:56
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://git.kernel.org/stable/c/01bdcc73dbe7be3ad4d4ee9a59b71e42f461a528 - Patch | |
| References | () https://git.kernel.org/stable/c/81b3374944d201872cfcf82730a7860f8e7c31dd - Patch | |
| References | () https://git.kernel.org/stable/c/aae109414a57ab4164218f36e2e4a17f027fcaaa - Patch | |
| References | () https://git.kernel.org/stable/c/b0c89ef025562161242a7c19b213bd6b272e93df - Patch | |
| References | () https://git.kernel.org/stable/c/da75dec7c6617bddad418159ffebcb133f008262 - Patch | |
| References | () https://git.kernel.org/stable/c/e4f4db47794c9f474b184ee1418f42e6a07412b6 - Patch | |
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 7.1 |
| CPE | cpe:2.3:o:linux:linux_kernel:5.14:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:5.14:rc6:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:5.14:rc7:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:5.14:-:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.2:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.2:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.2:rc3:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.2:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:5.14:rc5:*:*:*:*:*:* |
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| First Time |
Linux
Linux linux Kernel |
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| Summary |
|
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| CWE | NVD-CWE-noinfo |
27 Mar 2025, 17:15
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2025-03-27 17:15
Updated : 2026-01-22 20:56
NVD link : CVE-2023-53024
Mitre link : CVE-2023-53024
CVE.ORG link : CVE-2023-53024
JSON object : View
Products Affected
linux
- linux_kernel
CWE