Commit 00bc8988 authored by Leon Hwang's avatar Leon Hwang Committed by Alexei Starovoitov
Browse files

bpf, x86: Use emit_nops to replace memcpy x86_nops 



Move emit_nops() before emit_prologue() and replace
memcpy(prog, x86_nops[5], X86_PATCH_SIZE) with emit_nops(&prog, X86_PATCH_SIZE).

Signed-off-by: default avatarLeon Hwang <hffilwlqm@gmail.com>
Link: https://lore.kernel.org/r/20240104142226.87869-2-hffilwlqm@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 61a40c12

arch/x86/net/bpf_jit_comp.c

+22 −25
Original line number Diff line number Diff line
@@ -307,6 +307,25 @@ static void pop_callee_regs(u8 **pprog, bool *callee_regs_used) 
	*pprog = prog;

}



static void emit_nops(u8 **pprog, int len)

{

	u8 *prog = *pprog;

	int i, noplen;



	while (len > 0) {

		noplen = len;



		if (noplen > ASM_NOP_MAX)

			noplen = ASM_NOP_MAX;



		for (i = 0; i < noplen; i++)

			EMIT1(x86_nops[noplen][i]);

		len -= noplen;

	}



	*pprog = prog;

}



/*

 * Emit the various CFI preambles, see asm/cfi.h and the comments about FineIBT

 * in arch/x86/kernel/alternative.c
@@ -385,8 +404,7 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf, 
	/* BPF trampoline can be made to work without these nops,

	 * but let's waste 5 bytes for now and optimize later

	 */

	memcpy(prog, x86_nops[5], X86_PATCH_SIZE);

	prog += X86_PATCH_SIZE;

	emit_nops(&prog, X86_PATCH_SIZE);

	if (!ebpf_from_cbpf) {

		if (tail_call_reachable && !is_subprog)

			/* When it's the entry of the whole tailcall context,
@@ -692,8 +710,7 @@ static void emit_bpf_tail_call_direct(struct bpf_prog *bpf_prog, 
	if (stack_depth)

		EMIT3_off32(0x48, 0x81, 0xC4, round_up(stack_depth, 8));



	memcpy(prog, x86_nops[5], X86_PATCH_SIZE);

	prog += X86_PATCH_SIZE;

	emit_nops(&prog, X86_PATCH_SIZE);



	/* out: */

	ctx->tail_call_direct_label = prog - start;
@@ -1055,25 +1072,6 @@ static void detect_reg_usage(struct bpf_insn *insn, int insn_cnt, 
	}

}



static void emit_nops(u8 **pprog, int len)

{

	u8 *prog = *pprog;

	int i, noplen;



	while (len > 0) {

		noplen = len;



		if (noplen > ASM_NOP_MAX)

			noplen = ASM_NOP_MAX;



		for (i = 0; i < noplen; i++)

			EMIT1(x86_nops[noplen][i]);

		len -= noplen;

	}



	*pprog = prog;

}



/* emit the 3-byte VEX prefix

 *

 * r: same as rex.r, extra bit for ModRM reg field
@@ -2700,8 +2698,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im 
		/* remember return value in a stack for bpf prog to access */

		emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -8);

		im->ip_after_call = image + (prog - (u8 *)rw_image);

		memcpy(prog, x86_nops[5], X86_PATCH_SIZE);

		prog += X86_PATCH_SIZE;

		emit_nops(&prog, X86_PATCH_SIZE);

	}



	if (fmod_ret->nr_links) {