CVE-2026-98641

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

bpf, arm64: set up the frame pointer for the exception callback

A program acting as exception boundary saves all callee-saved registers,

so build_prologue() takes the exception_cb path and never calls

push_callee_regs(). That is the only place find_used_callee_regs() runs,

and with it the only place ctx->fp_used is set, so the callback prologue

does not emit the

mov x25, sp

that points BPF_REG_FP at the frame the callback runs on. x25 keeps

whatever it held when bpf_throw() was called. If the throw came from a

subprogram that uses its own BPF stack, that is the subprogram's frame

pointer, and since the subprogram never returns it never restores x25

either.

Stack accesses through BPF_REG_FP are rewritten to be stack pointer

relative, so those still land in the callback's own frame. Materializing

the register does not: a callback that passes the address of a local

variable to a helper hands over an address in the dead subprogram's

frame. That address is below the callback's stack pointer by then, and

the helper's own call chain covers it, so the helper can write over its

own return address. 0x1234 below is the value the helper was asked to

store:

pc : 0x1234

lr : 0x1234

Call trace:

0x1234 (P)

bpf_test_run+0x188/0x3e0

bpf_prog_test_run_skb+0x47c/0x998

__sys_bpf+0xbdc/0xdd8

Kernel panic - not syncing: Oops: Fatal exception in interrupt

Set ctx->fp_used on the exception callback path so that the existing code

further down sets x25 from the stack pointer. The epilogue restores it

from the main program's save area along with the other callee-saved

registers, as it already does. x86 sets the frame pointer for the

callback from the argument it is passed, and powerpc computes it from

the stack pointer.