ARM: net fix emit_udiv() for BPF_ALU | BPF_DIV | BPF_K intruction.

In that case, emit_udiv() will be called with rn == ARM_R0 (r_scratch)
and loading rm first into ARM_R0 will result in jit_udiv() function
being called the same dividend and divisor. Fix that by loading rn
first into ARM_R1 and then rm into ARM_R0.

Signed-off-by: Nicolas Schichan <nschichan@freebox.fr>
Cc: <stable@vger.kernel.org> # v3.13+
Fixes: aee636c4809f (bpf: do not use reciprocal divide)
Acked-by: Mircea Gherzan <mgherzan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index e1268f90502682c75dfd7a98e6ed15272ea8d512..f412b53ed268fbc0412479ca740055824b4ffc4a 100644 (file)
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -449,10 +449,21 @@ static inline void emit_udiv(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx)
                return;
        }
 #endif
-       if (rm != ARM_R0)
-               emit(ARM_MOV_R(ARM_R0, rm), ctx);
+
+       /*
+        * For BPF_ALU | BPF_DIV | BPF_K instructions, rm is ARM_R4
+        * (r_A) and rn is ARM_R0 (r_scratch) so load rn first into
+        * ARM_R1 to avoid accidentally overwriting ARM_R0 with rm
+        * before using it as a source for ARM_R1.
+        *
+        * For BPF_ALU | BPF_DIV | BPF_X rm is ARM_R4 (r_A) and rn is
+        * ARM_R5 (r_X) so there is no particular register overlap
+        * issues.
+        */
        if (rn != ARM_R1)
                emit(ARM_MOV_R(ARM_R1, rn), ctx);
+       if (rm != ARM_R0)
+               emit(ARM_MOV_R(ARM_R0, rm), ctx);
 
        ctx->seen |= SEEN_CALL;
        emit_mov_i(ARM_R3, (u32)jit_udiv, ctx);