| 1 | /* SPDX-License-Identifier: GPL-2.0-only */
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| 2 | /*
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| 3 | * Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org>
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| 4 | */
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| 5 |
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| 6 | |
| 7 | |
| 8 |
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| 9 | SYM_FUNC_START(__efi_rt_asm_wrapper)
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| 10 | stp x29, x30, [sp, |
| 11 | mov x29, sp
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| 12 |
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| 13 | /*
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| 14 | * Register x18 is designated as the 'platform' register by the AAPCS,
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| 15 | * which means firmware running at the same exception level as the OS
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| 16 | * (such as UEFI) should never touch it.
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| 17 | */
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| 18 | stp x1, x18, [sp, |
| 19 |
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| 20 | /*
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| 21 | * Preserve all callee saved registers and preserve the stack pointer
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| 22 | * value at the base of the EFI runtime stack so we can recover from
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| 23 | * synchronous exceptions occurring while executing the firmware
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| 24 | * routines.
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| 25 | */
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| 26 | stp x19, x20, [sp, |
| 27 | stp x21, x22, [sp, |
| 28 | stp x23, x24, [sp, |
| 29 | stp x25, x26, [sp, |
| 30 | stp x27, x28, [sp, |
| 31 |
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| 32 | ldr_l x16, efi_rt_stack_top
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| 33 | mov sp, x16
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| 34 | stp x18, x29, [sp, |
| 35 |
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| 36 | /*
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| 37 | * We are lucky enough that no EFI runtime services take more than
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| 38 | * 5 arguments, so all are passed in registers rather than via the
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| 39 | * stack.
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| 40 | */
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| 41 | mov x8, x0
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| 42 | mov x0, x2
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| 43 | mov x1, x3
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| 44 | mov x2, x4
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| 45 | mov x3, x5
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| 46 | mov x4, x6
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| 47 | blr x8
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| 48 |
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| 49 | mov x16, sp
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| 50 | mov sp, x29
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| 51 | str xzr, [x16, |
| 52 |
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| 53 | ldp x1, x2, [sp, |
| 54 | cmp x2, x18
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| 55 | ldp x29, x30, [sp], |
| 56 | b.ne 0f
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| 57 | ret
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| 58 | 0:
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| 59 | /*
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| 60 | * With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a
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| 61 | * shadow stack pointer, which we need to restore before returning to
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| 62 | * potentially instrumented code. This is safe because the wrapper is
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| 63 | * called with preemption disabled and a separate shadow stack is used
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| 64 | * for interrupts.
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| 65 | */
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| 66 | |
| 67 | ldr_l x18, efi_rt_stack_top
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| 68 | ldr x18, [x18, |
| 69 | |
| 70 |
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| 71 | b efi_handle_corrupted_x18 // tail call
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| 72 | SYM_FUNC_END(__efi_rt_asm_wrapper)
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| 73 |
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| 74 | SYM_CODE_START(__efi_rt_asm_recover)
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| 75 | mov sp, x30
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| 76 |
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| 77 | ldr_l x16, efi_rt_stack_top // clear recorded task SP value
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| 78 | str xzr, [x16, |
| 79 |
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| 80 | ldp x19, x20, [sp, |
| 81 | ldp x21, x22, [sp, |
| 82 | ldp x23, x24, [sp, |
| 83 | ldp x25, x26, [sp, |
| 84 | ldp x27, x28, [sp, |
| 85 | ldp x29, x30, [sp], |
| 86 | ret
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| 87 | SYM_CODE_END(__efi_rt_asm_recover)
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