Commit b0dc553c authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Borislav Petkov
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x86/fpu: Make the EFI FPU calling convention explicit 



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: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/25d392fff64680e0f4bb8cf0b1003314dc29eafe.1611205691.git.luto@kernel.org
parent 6ee1d745

arch/x86/include/asm/efi.h

+20 −4
Original line number Diff line number Diff line
@@ -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

arch/x86/platform/efi/efi_64.c

+2 −2
Original line number Diff line number Diff line
@@ -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);