Commit b114fcee authored by Puranjay Mohan's avatar Puranjay Mohan Committed by Daniel Borkmann
Browse files

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.

Fixes: 5d4fa9ec ("bpf, arm64: Avoid blindly saving/restoring all callee-saved registers")
Signed-off-by: default avatarPuranjay Mohan <puranjay@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarXu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/bpf/20250722133410.54161-2-puranjay@kernel.org
parent b7b3500b

arch/arm64/net/bpf_jit_comp.c

+1 −0
Original line number Diff line number Diff line
@@ -412,6 +412,7 @@ static void push_callee_regs(struct jit_ctx *ctx) 
		emit(A64_PUSH(A64_R(23), A64_R(24), A64_SP), ctx);

		emit(A64_PUSH(A64_R(25), A64_R(26), A64_SP), ctx);

		emit(A64_PUSH(A64_R(27), A64_R(28), A64_SP), ctx);

		ctx->fp_used = true;

	} else {

		find_used_callee_regs(ctx);

		for (i = 0; i + 1 < ctx->nr_used_callee_reg; i += 2) {