Re: [PATCH 2/3] net: bpf jit: x86: optimize choose_load_func error path

Vladimir Murzin
2013-10-13T14:21:57Z

On Fri, Oct 11, 2013 at 02:56:13PM -0400, David Miller wrote:
> From: Vladimir Murzin <murzin.v@gmail.com>
> Date: Tue, 8 Oct 2013 20:31:49 +0400
>
> > Macro CHOOSE_LOAD_FUNC returns handler for "any offset" if checks for K
> > were not passed. At the same time handlers for "any offset" cases make
> > the same checks against r_addr at run-time, that will always lead to
> > bpf_error.
> >
> > Run-time checks are still necessary for indirect load operations, but
> > error path for absolute and mesh loads are worth to optimize during bpf
> > compile time.
> >
> > Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
> >
> > Cc: Jan Seiffert <kaffeemonster@googlemail.com>
> > Cc: Eric Dumazet <edumazet@google.com>
> > Cc: "David S. Miller" <davem@davemloft.net
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> >
> > ---
> > arch/x86/net/bpf_jit_comp.c | 15 +++++++++------
> > 1 file changed, 9 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 79c216a..28ac17f 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -123,7 +123,7 @@ static inline void bpf_flush_icache(void *start, void *end)
> > }
> >
> > #define CHOOSE_LOAD_FUNC(K, func) \
> > - ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
> > + ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : NULL) : func##_positive_offset)
> >
> > /* Helper to find the offset of pkt_type in sk_buff
> > * We want to make sure its still a 3bit field starting at a byte boundary.
> > @@ -611,7 +611,13 @@ void bpf_jit_compile(struct sk_filter *fp)
> > }
> > case BPF_S_LD_W_ABS:
> > func = CHOOSE_LOAD_FUNC(K, sk_load_word);
> > -common_load: seen |= SEEN_DATAREF;
> > +common_load:
> > + if (!func) {
> > + CLEAR_A();
> > + EMIT_JMP(cleanup_addr - addrs[i]);
> > + break;
> > + }
> > + seen |= SEEN_DATAREF;
> > t_offset = func - (image + addrs[i]);
> > EMIT1_off32(0xbe, K); /* mov imm32,%esi */
> > EMIT1_off32(0xe8, t_offset); /* call */
> > @@ -625,10 +631,7 @@ common_load: seen |= SEEN_DATAREF;
> > case BPF_S_LDX_B_MSH:
> > func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
> > seen |= SEEN_DATAREF | SEEN_XREG;
> > - t_offset = func - (image + addrs[i]);
> > - EMIT1_off32(0xbe, K); /* mov imm32,%esi */
> > - EMIT1_off32(0xe8, t_offset); /* call sk_load_byte_msh */
> > - break;
> > + goto common_load;
>
> This second hunk will set SEEN_DATAREF even if common_load takes the
> !func path, that is not the intention at all here.
>
> There's a reason why these two code blocks aren't shared.

Thanks for review, David!

What about patch bellow?

---
arch/x86/net/bpf_jit_comp.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 79c216a..92128fe 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -123,7 +123,7 @@ static inline void bpf_flush_icache(void *start, void *end)
}

#define CHOOSE_LOAD_FUNC(K, func) \
- ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : func) : func##_positive_offset)
+ ((int)K < 0 ? ((int)K >= SKF_LL_OFF ? func##_negative_offset : NULL) : func##_positive_offset)

/* Helper to find the offset of pkt_type in sk_buff
* We want to make sure its still a 3bit field starting at a byte boundary.
@@ -611,7 +611,14 @@ void bpf_jit_compile(struct sk_filter *fp)
}
case BPF_S_LD_W_ABS:
func = CHOOSE_LOAD_FUNC(K, sk_load_word);
-common_load: seen |= SEEN_DATAREF;
+common_load:
+ if (!func) {
+ CLEAR_A();
+ EIT_JMP(cleanup_addr - addrs[i]);
+ break;
+ }
+
+ seen |= SEEN_DATAREF;
t_offset = func - (image + addrs[i]);
EMIT1_off32(0xbe, K); /* mov imm32,%esi */
EMIT1_off32(0xe8, t_offset); /* call */
@@ -624,6 +631,13 @@ common_load: seen |= SEEN_DATAREF;
goto common_load;
case BPF_S_LDX_B_MSH:
func = CHOOSE_LOAD_FUNC(K, sk_load_byte_msh);
+
+ if (!func) {
+ CLEAR_A();
+ EIT_JMP(cleanup_addr - addrs[i]);
+ break;
+ }
+
seen |= SEEN_DATAREF | SEEN_XREG;
t_offset = func - (image + addrs[i]);
EMIT1_off32(0xbe, K); /* mov imm32,%esi */
--
1.8.1.5

Vladimir