From: Alexei Starovoitov Date: Thu, 14 Nov 2019 18:57:13 +0000 (-0800) Subject: bpf: Reserve space for BPF trampoline in BPF programs X-Git-Tag: v5.5-rc1~174^2~49^2~12^2~7 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=9fd4a39dc7fe734d26eb89ea97e8c91331c6378c;p=linux.git 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 Signed-off-by: Daniel Borkmann Acked-by: Andrii Nakryiko Acked-by: Song Liu Link: https://lore.kernel.org/bpf/20191114185720.1641606-14-ast@kernel.org --- 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 */