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authorAlexei Starovoitov <ast@kernel.org>2019-11-14 10:57:13 -0800
committerDaniel Borkmann <daniel@iogearbox.net>2019-11-15 23:44:06 +0100
commit9fd4a39dc7fe734d26eb89ea97e8c91331c6378c (patch)
tree5783728bdca357b04e48d656d84eb07b1624a4a8 /arch/x86/net
parente76d776e9ca1fe266b3a7f8091eee5d1e635a545 (diff)
bpf: Reserve space for BPF trampoline in BPF programs
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
Diffstat (limited to 'arch/x86/net')
-rw-r--r--arch/x86/net/bpf_jit_comp.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index be2b43a894f6..c06096df9118 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -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 */