[3.19.y-ckt stable] Patch "ARM: net fix emit_udiv() for BPF_ALU | BPF_DIV | BPF_K intruction." has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 2b4b97766df337778b5257744c412d0d91ccdcbb Mon Sep 17 00:00:00 2001
From: Nicolas Schichan <nschichan at freebox.fr>
Date: Wed, 6 May 2015 18:31:56 +0200
Subject: ARM: net fix emit_udiv() for BPF_ALU | BPF_DIV | BPF_K intruction.

commit 19fc99d0c6ba7d9b65456496b5bb2169d5f74cd0 upstream.

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>
Fixes: aee636c4809f (bpf: do not use reciprocal divide)
Acked-by: Mircea Gherzan <mgherzan at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm/net/bpf_jit_32.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

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)
 		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);
--
1.9.1