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bpf: Reserve space for BPF trampoline in BPF programs

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BPF trampoline can be made to work with existing 5 bytes of BPF program
prologue, but let's add 5 bytes of NOPs to the beginning of every JITed BPF
program to make BPF trampoline job easier. They can be removed in the future.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20191114185720.1641606-14-ast@kernel.org
This commit is contained in:
Alexei Starovoitov 2019-11-14 10:57:13 -08:00 committed by Daniel Borkmann
parent e76d776e9c
commit 9fd4a39dc7
1 changed files with 7 additions and 2 deletions
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9
arch/x86/net/bpf_jit_comp.c
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@ -206,7 +206,7 @@ struct jit_context {
/* number of bytes emit_call() needs to generate call instruction */
#define X86_CALL_SIZE 5
#define PROLOGUE_SIZE 20
#define PROLOGUE_SIZE 25
/*
* Emit x86-64 prologue code for BPF program and check its size.
@ -215,8 +215,13 @@ struct jit_context {
static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf)
{
u8 *prog = *pprog;
int cnt = 0;
int cnt = X86_CALL_SIZE;
/* BPF trampoline can be made to work without these nops,
* but let's waste 5 bytes for now and optimize later
*/
memcpy(prog, ideal_nops[NOP_ATOMIC5], cnt);
prog += cnt;
EMIT1(0x55); /* push rbp */
EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */
/* sub rsp, rounded_stack_depth */