Bug 2389486 (CVE-2025-38586)

Summary: CVE-2025-38586 kernel: bpf, arm64: Fix fp initialization for exception boundary
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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Description OSIDB Bzimport 2025-08-19 18:03:30 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf, arm64: Fix fp initialization for exception boundary

In the ARM64 BPF JIT when prog->aux->exception_boundary is set for a BPF
program, find_used_callee_regs() is not called because for a program
acting as exception boundary, all callee saved registers are saved.
find_used_callee_regs() sets `ctx->fp_used = true;` when it sees FP
being used in any of the instructions.

For programs acting as exception boundary, ctx->fp_used remains false
even if frame pointer is used by the program and therefore, FP is not
set-up for such programs in the prologue. This can cause the kernel to
crash due to a pagefault.

Fix it by setting ctx->fp_used = true for exception boundary programs as
fp is always saved in such programs.
Comment 1 Jon Moroney 2025-08-19 22:52:56 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025081915-CVE-2025-38586-789b@gregkh/T