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x86/fpu: Make the EFI FPU calling convention explicit

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EFI uses kernel_fpu_begin() to conform to the UEFI calling convention.
This specifically requires initializing FCW (FPU Control Word), whereas
no sane 64-bit kernel code should use legacy 387 operations that
reference FCW.

This should allow to safely change the default semantics of
kernel_fpu_begin() to stop initializing FCW on 64-bit kernels.

 [ bp: Massage commit message a little. ]

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/25d392fff64680e0f4bb8cf0b1003314dc29eafe.1611205691.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski 2021-01-20 21:09:50 -08:00 committed by Borislav Petkov
parent 6ee1d745b7
commit b0dc553cfc
2 changed files with 22 additions and 6 deletions
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24
arch/x86/include/asm/efi.h
View File

@ -68,17 +68,33 @@ extern unsigned long efi_fw_vendor, efi_config_table;
#f " called with too many arguments (" #p ">" #n ")"); \
})
static inline void efi_fpu_begin(void)
{
/*
* The UEFI calling convention (UEFI spec 2.3.2 and 2.3.4) requires
* that FCW and MXCSR (64-bit) must be initialized prior to calling
* UEFI code. (Oddly the spec does not require that the FPU stack
* be empty.)
*/
kernel_fpu_begin_mask(KFPU_387 | KFPU_MXCSR);
}
static inline void efi_fpu_end(void)
{
kernel_fpu_end();
}
#ifdef CONFIG_X86_32
#define arch_efi_call_virt_setup() \
({ \
kernel_fpu_begin(); \
efi_fpu_begin(); \
firmware_restrict_branch_speculation_start(); \
})
#define arch_efi_call_virt_teardown() \
({ \
firmware_restrict_branch_speculation_end(); \
kernel_fpu_end(); \
efi_fpu_end(); \
})
#define arch_efi_call_virt(p, f, args...) p->f(args)
@ -107,7 +123,7 @@ struct efi_scratch {
#define arch_efi_call_virt_setup() \
({ \
efi_sync_low_kernel_mappings(); \
kernel_fpu_begin(); \
efi_fpu_begin(); \
firmware_restrict_branch_speculation_start(); \
efi_switch_mm(&efi_mm); \
})
@ -119,7 +135,7 @@ struct efi_scratch {
({ \
efi_switch_mm(efi_scratch.prev_mm); \
firmware_restrict_branch_speculation_end(); \
kernel_fpu_end(); \
efi_fpu_end(); \
})
#ifdef CONFIG_KASAN

4
arch/x86/platform/efi/efi_64.c
View File

@ -850,7 +850,7 @@ efi_set_virtual_address_map(unsigned long memory_map_size,
virtual_map);
efi_switch_mm(&efi_mm);
kernel_fpu_begin();
efi_fpu_begin();
/* Disable interrupts around EFI calls: */
local_irq_save(flags);
@ -859,7 +859,7 @@ efi_set_virtual_address_map(unsigned long memory_map_size,
descriptor_version, virtual_map);
local_irq_restore(flags);
kernel_fpu_end();
efi_fpu_end();
/* grab the virtually remapped EFI runtime services table pointer */
efi.runtime = READ_ONCE(systab->runtime);