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

Summary

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.

Timeline

1. Oct 18, 2026, 3:20 PM UTCCVE published
2. Oct 19, 2026, 9:23 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 5d4fa9ec5643a5c75d3c1e6abf50fb9284caf1ff · fixed in ecdd770a9fc3eaf6c3127c5991312b84774a7b0f; From 5d4fa9ec5643a5c75d3c1e6abf50fb9284caf1ff · fixed in b67b4c763f211e7a6391c356fef552e2ea63f08a; From 5d4fa9ec5643a5c75d3c1e6abf50fb9284caf1ff · fixed in d7cd5ebe13989f265015910faa25e5d50faa4c22; From 5d4fa9ec5643a5c75d3c1e6abf50fb9284caf1ff · fixed in ef1fb82f12186dd26153b14d9fbcf4ec98db81b3

• Linux Linux

  6.12

• KernelLinux

  From 6.12.0 · fixed in 6.12.112; From 6.13.0 · fixed in 6.18.55; From 6.19.0 · fixed in 7.2.9

References 4