[PATCH v2] ARM: net fix emit_udiv() for BPF_ALU | BPF_DIV | BPF_K intruction.
mgherzan at gmail.com
Sun May 10 04:31:26 PDT 2015
On 05/06/2015 06:31 PM, Nicolas Schichan wrote:
> 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 at freebox.fr>
> Cc: <stable at vger.kernel.org> # v3.13+
> Fixes: aee636c4809f (bpf: do not use reciprocal divide)
> arch/arm/net/bpf_jit_32.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
> This patch was part of a serie adding support to JITed seccomp filters
> to ARM but as it is an unrelated fix, it is more appropriate to send
> it separately.
> Changes from previous version: add a comment clarifying how
> emit_udiv() is called when translating BPF_ALU | BPF_DIV | BPF_K and
> BPF_ALU | BPF_DIV | BPF_X with respect to the rm and rn parameters.
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index e1268f9..f412b53 100644
> --- 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)
> - 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);
Acked-by: Mircea Gherzan <mgherzan at gmail.com>
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