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: 5d4fa9ec5643 ("bpf, arm64: Avoid blindly saving/restoring all callee-saved registers")
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/bpf/20250722133410.54161-2-puranjay@kernel.org

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 89b1b8c248c62e09cec61e13318d45b59006dce1..97ab651c0bd5dc9fdfbe66265c39f575a7534a11 100644 (file)
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -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) {