efi/x86: Simplify 64-bit EFI firmware call wrapper

The efi_call() wrapper used to invoke EFI runtime services serves
a number of purposes:
- realign the stack to 16 bytes
- preserve FP and CR0 register state
- translate from SysV to MS calling convention.

Preserving CR0.TS is no longer necessary in Linux, and preserving the
FP register state is also redundant in most cases, since efi_call() is
almost always used from within the scope of a pair of kernel_fpu_begin()/
kernel_fpu_end() calls, with the exception of the early call to
SetVirtualAddressMap() and the SGI UV support code.

So let's add a pair of kernel_fpu_begin()/_end() calls there as well,
and remove the unnecessary code from the assembly implementation of
efi_call(), and only keep the pieces that deal with the stack
alignment and the ABI translation.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Matthew Garrett <mjg59@google.com>
Cc: linux-efi@vger.kernel.org
Link: https://lkml.kernel.org/r/20200103113953.9571-10-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/platform/efi/Makefile

@@ -1,6 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
-OBJECT_FILES_NON_STANDARD_efi_stub_$(BITS).o := y
 
 obj-$(CONFIG_EFI) 		+= quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
 obj-$(CONFIG_EFI_MIXED)		+= efi_thunk_$(BITS).o

arch/x86/platform/efi/efi_64.c

@@ -1019,6 +1019,8 @@ efi_status_t __init efi_set_virtual_address_map(unsigned long memory_map_size,
 		efi_switch_mm(&efi_mm);
 	}
 
+	kernel_fpu_begin();
+
 	/* Disable interrupts around EFI calls: */
 	local_irq_save(flags);
 	status = efi_call(efi.systab->runtime->set_virtual_address_map,
@@ -1026,6 +1028,7 @@ efi_status_t __init efi_set_virtual_address_map(unsigned long memory_map_size,
 			  descriptor_version, virtual_map);
 	local_irq_restore(flags);
 
+	kernel_fpu_end();
 
 	if (save_pgd)
 		efi_old_memmap_phys_epilog(save_pgd);

arch/x86/platform/efi/efi_stub_64.S

@@ -8,41 +8,12 @@
  */
 
 #include <linux/linkage.h>
-#include <asm/segment.h>
+#include <asm/nospec-branch.h>
-#include <asm/msr.h>
-#include <asm/processor-flags.h>
-#include <asm/page_types.h>
-
-#define SAVE_XMM			\
-	mov %rsp, %rax;			\
-	subq $0x70, %rsp;		\
-	and $~0xf, %rsp;		\
-	mov %rax, (%rsp);		\
-	mov %cr0, %rax;			\
-	clts;				\
-	mov %rax, 0x8(%rsp);		\
-	movaps %xmm0, 0x60(%rsp);	\
-	movaps %xmm1, 0x50(%rsp);	\
-	movaps %xmm2, 0x40(%rsp);	\
-	movaps %xmm3, 0x30(%rsp);	\
-	movaps %xmm4, 0x20(%rsp);	\
-	movaps %xmm5, 0x10(%rsp)
-
-#define RESTORE_XMM			\
-	movaps 0x60(%rsp), %xmm0;	\
-	movaps 0x50(%rsp), %xmm1;	\
-	movaps 0x40(%rsp), %xmm2;	\
-	movaps 0x30(%rsp), %xmm3;	\
-	movaps 0x20(%rsp), %xmm4;	\
-	movaps 0x10(%rsp), %xmm5;	\
-	mov 0x8(%rsp), %rsi;		\
-	mov %rsi, %cr0;			\
-	mov (%rsp), %rsp
 
 SYM_FUNC_START(efi_call)
 	pushq %rbp
 	movq %rsp, %rbp
-	SAVE_XMM
+	and $~0xf, %rsp
 	mov 16(%rbp), %rax
 	subq $48, %rsp
 	mov %r9, 32(%rsp)
@@ -50,9 +21,7 @@ SYM_FUNC_START(efi_call)
 	mov %r8, %r9
 	mov %rcx, %r8
 	mov %rsi, %rcx
-	call *%rdi
+	CALL_NOSPEC %rdi
-	addq $48, %rsp
+	leave
-	RESTORE_XMM
-	popq %rbp
 	ret
 SYM_FUNC_END(efi_call)

arch/x86/platform/uv/bios_uv.c

@@ -34,10 +34,13 @@ static s64 __uv_bios_call(enum uv_bios_cmd which, u64 a1, u64 a2, u64 a3,
 	 * If EFI_OLD_MEMMAP is set, we need to fall back to using our old EFI
 	 * callback method, which uses efi_call() directly, with the kernel page tables:
 	 */
-	if (unlikely(efi_enabled(EFI_OLD_MEMMAP)))
+	if (unlikely(efi_enabled(EFI_OLD_MEMMAP))) {
+		kernel_fpu_begin();
 		ret = efi_call((void *)__va(tab->function), (u64)which, a1, a2, a3, a4, a5);
-	else
+		kernel_fpu_end();
+	} else {
 		ret = efi_call_virt_pointer(tab, function, (u64)which, a1, a2, a3, a4, a5);
+	}
 
 	return ret;
 }