From b0dc553cfc9d3bc2c7b8672b0b2fcf0edf0c3b6e Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 20 Jan 2021 21:09:50 -0800 Subject: [PATCH] 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: Andy Lutomirski Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/25d392fff64680e0f4bb8cf0b1003314dc29eafe.1611205691.git.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 c98f78330b09..c81e68f00071 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 e1e8d4e3a213..cf7b3bfe1a1e 100644 --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -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); -- 2.11.0