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: 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/20200103113953.9571-9-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index e29e5dc0b7506fd3ec72867f87e3d84a4ad0c223..cb08035b89a014e7f7c221b5a46683982caaab2a 100644 (file)
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -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();                                             \

diff --git a/arch/x86/platform/efi/efi_32.c b/arch/x86/platform/efi/efi_32.c
index 185950ade0e98b509edaaceead11e8566522e598..71dddd1620f98839aa65bdd6c3db56a8eaf7a675 100644 (file)
--- a/arch/x86/platform/efi/efi_32.c
+++ b/arch/x86/platform/efi/efi_32.c
@@ -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);

diff --git a/arch/x86/platform/efi/efi_stub_32.S b/arch/x86/platform/efi/efi_stub_32.S
index eed8b5b441f8c4e46b72ad36c1f84c5a2633afea..75c46e7a809f38ca96bfe5a9ebc473b7c87b5124 100644 (file)
--- a/arch/x86/platform/efi/efi_stub_32.S
+++ b/arch/x86/platform/efi/efi_stub_32.S
@@ -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)