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Date: Tue, 21 Jul 2015 14:14:13 +0200
From: Nicolas Schichan <nschichan@...ebox.fr>
To: "David S. Miller" <davem@...emloft.net>,
Daniel Borkmann <dborkman@...hat.com>,
Nicolas Schichan <nschichan@...ebox.fr>,
Mircea Gherzan <mgherzan@...il.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
netdev@...r.kernel.org
Cc: Russell King <linux@....linux.org.uk>,
Alexei Starovoitov <ast@...mgrid.com>
Subject: [PATCH V2 net 2/3] ARM: net: handle negative offsets in BPF JIT.
Previously, the JIT would reject negative offsets known during code
generation and mishandle negative offsets provided at runtime.
Fix that by calling bpf_internal_load_pointer_neg_helper()
appropriately in the jit_get_skb_{b,h,w} slow path helpers and by forcing
the execution flow to the slow path helpers when the offset is
negative.
Signed-off-by: Nicolas Schichan <nschichan@...ebox.fr>
---
arch/arm/net/bpf_jit_32.c | 47 ++++++++++++++++++++++++++++++++++++++---------
1 file changed, 38 insertions(+), 9 deletions(-)
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 21f5ace..d9b2524 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -74,32 +74,52 @@ struct jit_ctx {
int bpf_jit_enable __read_mostly;
-static u64 jit_get_skb_b(struct sk_buff *skb, unsigned offset)
+static inline int call_neg_helper(struct sk_buff *skb, int offset, void *ret,
+ unsigned int size)
+{
+ void *ptr = bpf_internal_load_pointer_neg_helper(skb, offset, size);
+
+ if (!ptr)
+ return -EFAULT;
+ memcpy(ret, ptr, size);
+ return 0;
+}
+
+static u64 jit_get_skb_b(struct sk_buff *skb, int offset)
{
u8 ret;
int err;
- err = skb_copy_bits(skb, offset, &ret, 1);
+ if (offset < 0)
+ err = call_neg_helper(skb, offset, &ret, 1);
+ else
+ err = skb_copy_bits(skb, offset, &ret, 1);
return (u64)err << 32 | ret;
}
-static u64 jit_get_skb_h(struct sk_buff *skb, unsigned offset)
+static u64 jit_get_skb_h(struct sk_buff *skb, int offset)
{
u16 ret;
int err;
- err = skb_copy_bits(skb, offset, &ret, 2);
+ if (offset < 0)
+ err = call_neg_helper(skb, offset, &ret, 2);
+ else
+ err = skb_copy_bits(skb, offset, &ret, 2);
return (u64)err << 32 | ntohs(ret);
}
-static u64 jit_get_skb_w(struct sk_buff *skb, unsigned offset)
+static u64 jit_get_skb_w(struct sk_buff *skb, int offset)
{
u32 ret;
int err;
- err = skb_copy_bits(skb, offset, &ret, 4);
+ if (offset < 0)
+ err = call_neg_helper(skb, offset, &ret, 4);
+ else
+ err = skb_copy_bits(skb, offset, &ret, 4);
return (u64)err << 32 | ntohl(ret);
}
@@ -536,9 +556,6 @@ static int build_body(struct jit_ctx *ctx)
case BPF_LD | BPF_B | BPF_ABS:
load_order = 0;
load:
- /* the interpreter will deal with the negative K */
- if ((int)k < 0)
- return -ENOTSUPP;
emit_mov_i(r_off, k, ctx);
load_common:
ctx->seen |= SEEN_DATA | SEEN_CALL;
@@ -553,6 +570,18 @@ load_common:
condt = ARM_COND_HI;
}
+ /*
+ * test for negative offset, only if we are
+ * currently scheduled to take the fast
+ * path. this will update the flags so that
+ * the slowpath instruction are ignored if the
+ * offset is negative.
+ *
+ * for loard_order == 0 the HI condition will
+ * make loads at offset 0 take the slow path too.
+ */
+ _emit(condt, ARM_CMP_I(r_off, 0), ctx);
+
_emit(condt, ARM_ADD_R(r_scratch, r_off, r_skb_data),
ctx);
--
1.9.1
--
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