diff options
Diffstat (limited to 'arch/arm64/kernel/efi-rt-wrapper.S')
| -rw-r--r-- | arch/arm64/kernel/efi-rt-wrapper.S | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S new file mode 100644 index 000000000..2d3c4b023 --- /dev/null +++ b/arch/arm64/kernel/efi-rt-wrapper.S @@ -0,0 +1,59 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org> + */ + +#include <linux/linkage.h> +#include <asm/assembler.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] + + ldr_l x16, efi_rt_stack_top + mov sp, x16 +#ifdef CONFIG_SHADOW_CALL_STACK + str x18, [sp, #-16]! +#endif + + /* + * 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 + + mov sp, x29 + 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. + */ +#ifdef CONFIG_SHADOW_CALL_STACK + ldr_l x18, efi_rt_stack_top + ldr x18, [x18, #-16] +#endif + + b efi_handle_corrupted_x18 // tail call +SYM_FUNC_END(__efi_rt_asm_wrapper) |