[PATCH v4 bpf-next 13/20] bpf: Reserve space for BPF trampoline in BPF programs
From: Alexei Starovoitov <ast@kernel.org>
Date: 2019-11-14 18:57:52
Also in:
bpf
Subsystem:
bpf jit for x86 64-bit, bpf [general] (safe dynamic programs and tools), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
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> Acked-by: Andrii Nakryiko <redacted> Acked-by: Song Liu <redacted> --- arch/x86/net/bpf_jit_comp.c | 9 +++++++-- 1 file 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 */
--
2.23.0