Commit 16175375 authored by Puranjay Mohan's avatar Puranjay Mohan Committed by Alexei Starovoitov
Browse files

bpf, arm64: Add JIT support for timed may_goto 



When verifier sees a timed may_goto instruction, it emits a call to
arch_bpf_timed_may_goto() with a stack offset in BPF_REG_AX (arm64 r9)
and expects a count value to be returned in the same register. The
verifier doesn't save or restore any registers before emitting this
call.

arch_bpf_timed_may_goto() should act as a trampoline to call
bpf_check_timed_may_goto() with AAPCS64 calling convention.

To support this custom calling convention, implement
arch_bpf_timed_may_goto() in assembly and make sure BPF caller saved
registers are saved and restored, call bpf_check_timed_may_goto with
arm64 calling convention where first argument and return value both are
in x0, then put the result back into BPF_REG_AX before returning.

Signed-off-by: default avatarPuranjay Mohan <puranjay@kernel.org>
Acked-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: default avatarXu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/r/20250827113245.52629-2-puranjay@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 4c229f33

arch/arm64/net/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -2,4 +2,4 @@ 
#

# ARM64 networking code

#

obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o
 
obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o bpf_timed_may_goto.o

arch/arm64/net/bpf_jit_comp.c

+12 −1
Original line number Diff line number Diff line
@@ -1558,6 +1558,12 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, 
		if (ret < 0)

			return ret;

		emit_call(func_addr, ctx);

		/*

		 * Call to arch_bpf_timed_may_goto() is emitted by the

		 * verifier and called with custom calling convention with

		 * first argument and return value in BPF_REG_AX (x9).

		 */

		if (func_addr != (u64)arch_bpf_timed_may_goto)

			emit(A64_MOV(1, r0, A64_R(0)), ctx);

		break;

	}
@@ -3038,6 +3044,11 @@ bool bpf_jit_bypass_spec_v4(void) 
	return true;

}



bool bpf_jit_supports_timed_may_goto(void)

{

	return true;

}



bool bpf_jit_inlines_helper_call(s32 imm)

{

	switch (imm) {

arch/arm64/net/bpf_timed_may_goto.S

0 → 100644
+40 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

/* Copyright (c) 2025 Puranjay Mohan <puranjay@kernel.org> */



#include <linux/linkage.h>



SYM_FUNC_START(arch_bpf_timed_may_goto)

	/* Allocate stack space and emit frame record */

	stp     x29, x30, [sp, #-64]!

	mov     x29, sp



	/* Save BPF registers R0 - R5 (x7, x0-x4)*/

	stp	x7, x0, [sp, #16]

	stp	x1, x2, [sp, #32]

	stp	x3, x4, [sp, #48]



	/*

	 * Stack depth was passed in BPF_REG_AX (x9), add it to the BPF_FP

	 * (x25) to get the pointer to count and timestamp and pass it as the

	 * first argument in x0.

	 *

	 * Before generating the call to arch_bpf_timed_may_goto, the verifier

	 * generates a load instruction using FP, i.e. REG_AX = *(u64 *)(FP -

	 * stack_off_cnt), so BPF_REG_FP (x25) is always set up by the arm64

	 * jit in this case.

	 */

	add	x0, x9, x25

	bl	bpf_check_timed_may_goto

	/* BPF_REG_AX(x9) will be stored into count, so move return value to it. */

	mov	x9, x0



	/* Restore BPF registers R0 - R5 (x7, x0-x4) */

	ldp	x7, x0, [sp, #16]

	ldp	x1, x2, [sp, #32]

	ldp	x3, x4, [sp, #48]



	/* Restore FP and LR */

	ldp     x29, x30, [sp], #64



	ret

SYM_FUNC_END(arch_bpf_timed_may_goto)