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: 19d3c179a377 ("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

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 8bbd0b20136a87fe746592f8f3ed09cb70e89cd6..5db82bfc9dc1156c37ac4a87ce0e880e61542dd7 100644 (file)
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -2220,7 +2220,11 @@ 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) {
-               emit_a64_mov_i64(A64_R(0), (const u64)im, ctx);
+               /* 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);
        }
 
@@ -2264,7 +2268,11 @@ 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;
-               emit_a64_mov_i64(A64_R(0), (const u64)im, ctx);
+               /* 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);
        }