Messages in this thread Patch in this message | | | From | Andy Lutomirski <> | Subject | [PATCH v3 3/4] x86/fpu: Make the EFI FPU calling convention explicit | Date | Wed, 20 Jan 2021 21:09:50 -0800 |
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EFI uses kernel_fpu_begin() to conform to the UEFI calling convention. This specifically requires initializing FCW, whereas no sane 64-bit kernel code should use legacy 387 operations that reference FCW.
This should enable us to safely change the default semantics of kernel_fpu_begin() to stop initializing FCW on 64-bit kernels.
Cc: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/x86/include/asm/efi.h | 24 ++++++++++++++++++++---- arch/x86/platform/efi/efi_64.c | 4 ++-- 2 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h index bc9758ef292e..f3201544fbf8 100644 --- a/arch/x86/include/asm/efi.h +++ b/arch/x86/include/asm/efi.h @@ -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 diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c index 8f5759df7776..f042040b5da1 100644 --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -848,7 +848,7 @@ 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); @@ -857,7 +857,7 @@ 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); -- 2.29.2
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