efi-rt-wrapper.S
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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org>
*/
#include <linux/linkage.h>
SYM_FUNC_START(__efi_rt_asm_wrapper)
stp x29, x30, [sp, #-32]!
mov x29, sp
/*
* Register x18 is designated as the 'platform' register by the AAPCS,
* which means firmware running at the same exception level as the OS
* (such as UEFI) should never touch it.
*/
stp x1, x18, [sp, #16]
/*
* We are lucky enough that no EFI runtime services take more than
* 5 arguments, so all are passed in registers rather than via the
* stack.
*/
mov x8, x0
mov x0, x2
mov x1, x3
mov x2, x4
mov x3, x5
mov x4, x6
blr x8
ldp x1, x2, [sp, #16]
cmp x2, x18
ldp x29, x30, [sp], #32
b.ne 0f
ret
0:
/*
* With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a
* shadow stack pointer, which we need to restore before returning to
* potentially instrumented code. This is safe because the wrapper is
* called with preemption disabled and a separate shadow stack is used
* for interrupts.
*/
mov x18, x2
b efi_handle_corrupted_x18 // tail call
SYM_FUNC_END(__efi_rt_asm_wrapper)