Commit a46d6740 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
Browse files

efi/x86: Simplify i386 efi_call_phys() firmware call wrapper 



The variadic efi_call_phys() wrapper that exists on i386 was
originally created to call into any EFI firmware runtime service,
but in practice, we only use it once, to call SetVirtualAddressMap()
during early boot.
The flexibility provided by the variadic nature also makes it
type unsafe, and makes the assembler code more complicated than
needed, since it has to deal with an unknown number of arguments
living on the stack.

So clean this up, by renaming the helper to efi_call_svam(), and
dropping the unneeded complexity. Let's also drop the reference
to the efi_phys struct and grab the address from the EFI system
table directly.

Signed-off-by: default avatarArd 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/20200103113953.9571-9-ardb@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 69829470

arch/x86/include/asm/efi.h

+0 −3
Original line number Diff line number Diff line
@@ -35,9 +35,6 @@ 
#define ARCH_EFI_IRQ_FLAGS_MASK	X86_EFLAGS_IF



#ifdef CONFIG_X86_32



extern asmlinkage unsigned long efi_call_phys(void *, ...);



#define arch_efi_call_virt_setup()					\

({									\

	kernel_fpu_begin();						\

arch/x86/platform/efi/efi_32.c

+3 −2
Original line number Diff line number Diff line
@@ -66,7 +66,8 @@ void __init efi_map_region(efi_memory_desc_t *md) 
void __init efi_map_region_fixed(efi_memory_desc_t *md) {}

void __init parse_efi_setup(u64 phys_addr, u32 data_len) {}



extern struct efi efi_phys;

efi_status_t efi_call_svam(efi_set_virtual_address_map_t *__efiapi *,

			   u32, u32, u32, void *);



efi_status_t __init efi_set_virtual_address_map(unsigned long memory_map_size,

						unsigned long descriptor_size,
@@ -89,7 +90,7 @@ efi_status_t __init efi_set_virtual_address_map(unsigned long memory_map_size, 


	/* Disable interrupts around EFI calls: */

	local_irq_save(flags);

	status = efi_call_phys(efi_phys.set_virtual_address_map,

	status = efi_call_svam(&efi.systab->runtime->set_virtual_address_map,

			       memory_map_size, descriptor_size,

			       descriptor_version, virtual_map);

	local_irq_restore(flags);

arch/x86/platform/efi/efi_stub_32.S

+17 −92
Original line number Diff line number Diff line
@@ -7,118 +7,43 @@ 
 */



#include <linux/linkage.h>

#include <linux/init.h>

#include <asm/page_types.h>



/*

 * efi_call_phys(void *, ...) is a function with variable parameters.

 * All the callers of this function assure that all the parameters are 4-bytes.

 */



/*

 * In gcc calling convention, EBX, ESP, EBP, ESI and EDI are all callee save.

 * So we'd better save all of them at the beginning of this function and restore

 * at the end no matter how many we use, because we can not assure EFI runtime

 * service functions will comply with gcc calling convention, too.

 */

	__INIT

SYM_FUNC_START(efi_call_svam)

	push	8(%esp)

	push	8(%esp)

	push	%ecx

	push	%edx



.text

SYM_FUNC_START(efi_call_phys)

	/*

	 * 0. The function can only be called in Linux kernel. So CS has been

	 * set to 0x0010, DS and SS have been set to 0x0018. In EFI, I found

	 * the values of these registers are the same. And, the corresponding

	 * GDT entries are identical. So I will do nothing about segment reg

	 * and GDT, but change GDT base register in prolog and epilog.

	 */



	/*

	 * 1. Now I am running with EIP = <physical address> + PAGE_OFFSET.

	 * But to make it smoothly switch from virtual mode to flat mode.

	 * The mapping of lower virtual memory has been created in prolog and

	 * epilog.

	 * Switch to the flat mapped alias of this routine, by jumping to the

	 * address of label '1' after subtracting PAGE_OFFSET from it.

	 */

	movl	$1f, %edx

	subl	$__PAGE_OFFSET, %edx

	jmp	*%edx

1:



	/*

	 * 2. Now on the top of stack is the return

	 * address in the caller of efi_call_phys(), then parameter 1,

	 * parameter 2, ..., param n. To make things easy, we save the return

	 * address of efi_call_phys in a global variable.

	 */

	popl	%edx

	movl	%edx, saved_return_addr

	/* get the function pointer into ECX*/

	popl	%ecx

	movl	%ecx, efi_rt_function_ptr

	movl	$2f, %edx

	subl	$__PAGE_OFFSET, %edx

	pushl	%edx



	/*

	 * 3. Clear PG bit in %CR0.

	 */

	/* disable paging */

	movl	%cr0, %edx

	andl	$0x7fffffff, %edx

	movl	%edx, %cr0

	jmp	1f

1:



	/*

	 * 4. Adjust stack pointer.

	 */

	/* convert the stack pointer to a flat mapped address */

	subl	$__PAGE_OFFSET, %esp



	/*

	 * 5. Call the physical function.

	 */

	jmp	*%ecx

	/* call the EFI routine */

	call	*(%eax)



2:

	/*

	 * 6. After EFI runtime service returns, control will return to

	 * following instruction. We'd better readjust stack pointer first.

	 */

	addl	$__PAGE_OFFSET, %esp

	/* convert ESP back to a kernel VA, and pop the outgoing args */

	addl	$__PAGE_OFFSET + 16, %esp



	/*

	 * 7. Restore PG bit

	 */

	/* re-enable paging */

	movl	%cr0, %edx

	orl	$0x80000000, %edx

	movl	%edx, %cr0

	jmp	1f

1:

	/*

	 * 8. Now restore the virtual mode from flat mode by

	 * adding EIP with PAGE_OFFSET.

	 */

	movl	$1f, %edx

	jmp	*%edx

1:



	/*

	 * 9. Balance the stack. And because EAX contain the return value,

	 * we'd better not clobber it.

	 */

	leal	efi_rt_function_ptr, %edx

	movl	(%edx), %ecx

	pushl	%ecx



	/*

	 * 10. Push the saved return address onto the stack and return.

	 */

	leal	saved_return_addr, %edx

	movl	(%edx), %ecx

	pushl	%ecx

	ret

SYM_FUNC_END(efi_call_phys)

.previous



.data

saved_return_addr:

	.long 0

efi_rt_function_ptr:

	.long 0
 
SYM_FUNC_END(efi_call_svam)

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