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efi/arm64: Check whether x18 is preserved by runtime services calls

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Whether or not we will ever decide to start using x18 as a platform
register in Linux is uncertain, but by that time, we will need to
ensure that UEFI runtime services calls don't corrupt it.

So let's start issuing warnings now for this, and increase the
likelihood that these firmware images have all been replaced by that time.

This has been fixed on the EDK2 side in commit:

  6d73863b5464 ("BaseTools/tools_def AARCH64: mark register x18 as reserved")

dated July 13, 2017.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20180308080020.22828-6-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ard Biesheuvel 2018-03-08 08:00:13 +00:00 committed by Ingo Molnar
parent 1832e64162
commit 7e611e7dbb
4 changed files with 52 additions and 2 deletions
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4
arch/arm64/include/asm/efi.h
View file

@ -31,7 +31,7 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
({ \
efi_##f##_t *__f; \
__f = p->f; \
__f(args); \
__efi_rt_asm_wrapper(__f, #f, args); \
})
#define arch_efi_call_virt_teardown() \
@ -40,6 +40,8 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
efi_virtmap_unload(); \
})
efi_status_t __efi_rt_asm_wrapper(void *, const char *, ...);
#define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
/* arch specific definitions used by the stub code */

3
arch/arm64/kernel/Makefile
View file

@ -38,7 +38,8 @@ arm64-obj-$(CONFIG_CPU_PM) += sleep.o suspend.o
arm64-obj-$(CONFIG_CPU_IDLE) += cpuidle.o
arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o
arm64-obj-$(CONFIG_KGDB) += kgdb.o
arm64-obj-$(CONFIG_EFI) += efi.o efi-entry.stub.o
arm64-obj-$(CONFIG_EFI) += efi.o efi-entry.stub.o \
efi-rt-wrapper.o
arm64-obj-$(CONFIG_PCI) += pci.o
arm64-obj-$(CONFIG_ARMV8_DEPRECATED) += armv8_deprecated.o
arm64-obj-$(CONFIG_ACPI) += acpi.o

41
arch/arm64/kernel/efi-rt-wrapper.S Normal file
View file

@ -0,0 +1,41 @@
/*
* Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/linkage.h>
ENTRY(__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: b efi_handle_corrupted_x18 // tail call
ENDPROC(__efi_rt_asm_wrapper)

6
arch/arm64/kernel/efi.c
View file

@ -126,3 +126,9 @@ bool efi_poweroff_required(void)
{
return efi_enabled(EFI_RUNTIME_SERVICES);
}
asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f)
{
pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f);
return s;
}