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bpf: change x86 JITed program stack layout

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in order to JIT programs with different stack sizes we need to
make epilogue and exception path to be stack size independent,
hence move auxiliary stack space from the bottom of the stack
to the top of the stack.
Nice side effect is that JITed function prologue becomes shorter
due to imm8 offset encoding vs imm32.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov
2017-05-30 13:31:34 -07:00
committed by David S. Miller
parent b870aa901f
commit 177366bf7c
2 changed files with 39 additions and 37 deletions
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20
arch/x86/net/bpf_jit.S
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@@ -19,9 +19,6 @@
*/
#define SKBDATA %r10
#define SKF_MAX_NEG_OFF $(-0x200000) /* SKF_LL_OFF from filter.h */
#define MAX_BPF_STACK (512 /* from filter.h */ + \
32 /* space for rbx,r13,r14,r15 */ + \
8 /* space for skb_copy_bits */)
#define FUNC(name) \
.globl name; \
@@ -66,7 +63,7 @@ FUNC(sk_load_byte_positive_offset)
/* rsi contains offset and can be scratched */
#define bpf_slow_path_common(LEN) \
lea -MAX_BPF_STACK + 32(%rbp), %rdx;\
lea 32(%rbp), %rdx;\
FRAME_BEGIN; \
mov %rbx, %rdi; /* arg1 == skb */ \
push %r9; \
@@ -83,14 +80,14 @@ FUNC(sk_load_byte_positive_offset)
bpf_slow_path_word:
bpf_slow_path_common(4)
js bpf_error
mov - MAX_BPF_STACK + 32(%rbp),%eax
mov 32(%rbp),%eax
bswap %eax
ret
bpf_slow_path_half:
bpf_slow_path_common(2)
js bpf_error
mov - MAX_BPF_STACK + 32(%rbp),%ax
mov 32(%rbp),%ax
rol $8,%ax
movzwl %ax,%eax
ret
@@ -98,7 +95,7 @@ bpf_slow_path_half:
bpf_slow_path_byte:
bpf_slow_path_common(1)
js bpf_error
movzbl - MAX_BPF_STACK + 32(%rbp),%eax
movzbl 32(%rbp),%eax
ret
#define sk_negative_common(SIZE) \
@@ -148,9 +145,10 @@ FUNC(sk_load_byte_negative_offset)
bpf_error:
# force a return 0 from jit handler
xor %eax,%eax
mov - MAX_BPF_STACK(%rbp),%rbx
mov - MAX_BPF_STACK + 8(%rbp),%r13
mov - MAX_BPF_STACK + 16(%rbp),%r14
mov - MAX_BPF_STACK + 24(%rbp),%r15
mov (%rbp),%rbx
mov 8(%rbp),%r13
mov 16(%rbp),%r14
mov 24(%rbp),%r15
add $40, %rbp
leaveq
ret