1/* SPDX-License-Identifier: GPL-2.0-only */ 2/* 3 * Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org> 4 */ 5 6#include <linux/linkage.h> 7#include <asm/assembler.h> 8 9SYM_FUNC_START(__efi_rt_asm_wrapper) 10 stp x29, x30, [sp, #-32]! 11 mov x29, sp 12 13 /* 14 * Register x18 is designated as the 'platform' register by the AAPCS, 15 * which means firmware running at the same exception level as the OS 16 * (such as UEFI) should never touch it. 17 */ 18 stp x1, x18, [sp, #16] 19 20 ldr_l x16, efi_rt_stack_top 21 mov sp, x16 22#ifdef CONFIG_SHADOW_CALL_STACK 23 str x18, [sp, #-16]! 24#endif 25 26 /* 27 * We are lucky enough that no EFI runtime services take more than 28 * 5 arguments, so all are passed in registers rather than via the 29 * stack. 30 */ 31 mov x8, x0 32 mov x0, x2 33 mov x1, x3 34 mov x2, x4 35 mov x3, x5 36 mov x4, x6 37 blr x8 38 39 mov sp, x29 40 ldp x1, x2, [sp, #16] 41 cmp x2, x18 42 ldp x29, x30, [sp], #32 43 b.ne 0f 44 ret 450: 46 /* 47 * With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a 48 * shadow stack pointer, which we need to restore before returning to 49 * potentially instrumented code. This is safe because the wrapper is 50 * called with preemption disabled and a separate shadow stack is used 51 * for interrupts. 52 */ 53#ifdef CONFIG_SHADOW_CALL_STACK 54 ldr_l x18, efi_rt_stack_top 55 ldr x18, [x18, #-16] 56#endif 57 58 b efi_handle_corrupted_x18 // tail call 59SYM_FUNC_END(__efi_rt_asm_wrapper) 60