bpf, arm64: Fix fp initialization for exception boundary

Vulnerability Description

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.

References

• https://git.kernel.org/stable/c/0dbef493cae7d451f740558665893c000adb2321
• https://git.kernel.org/stable/c/e23184725dbb72d5d02940222eee36dbba2aa422
• https://git.kernel.org/stable/c/1ce30231e0a2c8c361ee5f8f7f265fc17130adce
• https://git.kernel.org/stable/c/b114fcee766d5101eada1aca7bb5fd0a86c89b35