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[PATCH 05/17] MIPS: bpf: Return error code if the offset is a negative n

To: <linux-mips@linux-mips.org>
Subject: [PATCH 05/17] MIPS: bpf: Return error code if the offset is a negative number
From: Markos Chandras <markos.chandras@imgtec.com>
Date: Mon, 23 Jun 2014 10:38:48 +0100
Cc: Markos Chandras <markos.chandras@imgtec.com>, "David S. Miller" <davem@davemloft.net>, Daniel Borkmann <dborkman@redhat.com>, "Alexei Starovoitov" <ast@plumgrid.com>, <netdev@vger.kernel.org>
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Previously, the negative offset was not checked leading to failures
due to trying to load data beyond the skb struct boundaries. Until we
have proper asm helpers in place, it's best if we return ENOSUPP if K
is negative when trying to JIT the filter or 0 during runtime if we
do an indirect load where the value of X is unknown during build time.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
---
 arch/mips/net/bpf_jit.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
index 5cc92c4590cb..95728ea6cb74 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c
@@ -331,6 +331,12 @@ static inline void emit_srl(unsigned int dst, unsigned int 
src,
        emit_instr(ctx, srl, dst, src, sa);
 }
 
+static inline void emit_slt(unsigned int dst, unsigned int src1,
+                           unsigned int src2, struct jit_ctx *ctx)
+{
+       emit_instr(ctx, slt, dst, src1, src2);
+}
+
 static inline void emit_sltu(unsigned int dst, unsigned int src1,
                             unsigned int src2, struct jit_ctx *ctx)
 {
@@ -816,8 +822,21 @@ static int build_body(struct jit_ctx *ctx)
                        /* A <- P[k:1] */
                        load_order = 0;
 load:
+                       /* the interpreter will deal with the negative K */
+                       if ((int)k < 0)
+                               return -ENOTSUPP;
+
                        emit_load_imm(r_off, k, ctx);
 load_common:
+                       /*
+                        * We may got here from the indirect loads so
+                        * return if offset is negative.
+                        */
+                       emit_slt(r_s0, r_off, r_zero, ctx);
+                       emit_bcond(MIPS_COND_NE, r_s0, r_zero,
+                                  b_imm(prog->len, ctx), ctx);
+                       emit_reg_move(r_ret, r_zero, ctx);
+
                        ctx->flags |= SEEN_CALL | SEEN_OFF | SEEN_S0 |
                                SEEN_SKB | SEEN_A;
 
@@ -880,6 +899,10 @@ load_ind:
                        emit_load(r_X, r_skb, off, ctx);
                        break;
                case BPF_LDX | BPF_B | BPF_MSH:
+                       /* the interpreter will deal with the negative K */
+                       if ((int)k < 0)
+                               return -ENOTSUPP;
+
                        /* X <- 4 * (P[k:1] & 0xf) */
                        ctx->flags |= SEEN_X | SEEN_CALL | SEEN_S0 | SEEN_SKB;
                        /* Load offset to a1 */
-- 
2.0.0


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