Commit a552e2ef authored Oct 18, 2024 by Peter Collingbourne Committed by Daniel Borkmann Oct 21, 2024

bpf, arm64: Fix address emission with tag-based KASAN enabled

When BPF_TRAMP_F_CALL_ORIG is enabled, the address of a bpf_tramp_image
struct on the stack is passed during the size calculation pass and
an address on the heap is passed during code generation. This may
cause a heap buffer overflow if the heap address is tagged because
emit_a64_mov_i64() will emit longer code than it did during the size
calculation pass. The same problem could occur without tag-based
KASAN if one of the 16-bit words of the stack address happened to
be all-ones during the size calculation pass. Fix the problem by
assuming the worst case (4 instructions) when calculating the size
of the bpf_tramp_image address emission.

Fixes: 19d3c179 ("bpf, arm64: Fix trampoline for BPF_TRAMP_F_CALL_ORIG")
Signed-off-by: Peter Collingbourne <pcc@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://linux-review.googlesource.com/id/I1496f2bc24fba7a1d492e16e2b94cf43714f2d3c
Link: https://lore.kernel.org/bpf/20241018221644.3240898-1-pcc@google.com

parent 42f7652d

arch/arm64/net/bpf_jit_comp.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -2220,6 +2220,10 @@ static int prepare_trampoline(struct jit_ctx ctx, struct bpf_tramp_image im,
		emit(A64_STR64I(A64_R(20), A64_SP, regs_off + 8), ctx);

		if (flags & BPF_TRAMP_F_CALL_ORIG) {
		/* for the first pass, assume the worst case */
		if (!ctx->image)
		ctx->idx += 4;
		else
		emit_a64_mov_i64(A64_R(0), (const u64)im, ctx);
		emit_call((const u64)__bpf_tramp_enter, ctx);
		}
		@@ -2264,6 +2268,10 @@ static int prepare_trampoline(struct jit_ctx ctx, struct bpf_tramp_image im,

		if (flags & BPF_TRAMP_F_CALL_ORIG) {
		im->ip_epilogue = ctx->ro_image + ctx->idx;
		/* for the first pass, assume the worst case */
		if (!ctx->image)
		ctx->idx += 4;
		else
		emit_a64_mov_i64(A64_R(0), (const u64)im, ctx);
		emit_call((const u64)__bpf_tramp_exit, ctx);
		}