efi/x86: Setup stack correctly for efi_pe_entry

Commit

  17054f492dfd ("efi/x86: Implement mixed mode boot without the handover protocol")

introduced a new entry point for the EFI stub to be booted in mixed mode
on 32-bit firmware.

When entered via efi32_pe_entry, control is first transferred to
startup_32 to setup for the switch to long mode, and then the EFI stub
proper is entered via efi_pe_entry. efi_pe_entry is an MS ABI function,
and the ABI requires 32 bytes of shadow stack space to be allocated by
the caller, as well as the stack being aligned to 8 mod 16 on entry.

Allocate 40 bytes on the stack before switching to 64-bit mode when
calling efi_pe_entry to account for this.

For robustness, explicitly align boot_stack_end to 16 bytes. It is
currently implicitly aligned since .bss is cacheline-size aligned,
head_64.o is the first object file with a .bss section, and the heap and
boot sizes are aligned.

Fixes: 17054f492dfd ("efi/x86: Implement mixed mode boot without the handover protocol")
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200617131957.2507632-1-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index e821a7d..97d37f0 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -213,7 +213,6 @@ SYM_FUNC_START(startup_32)
         * We place all of the values on our mini stack so lret can
         * used to perform that far jump.
         */
-       pushl   $__KERNEL_CS
        leal    startup_64(%ebp), %eax
 #ifdef CONFIG_EFI_MIXED
        movl    efi32_boot_args(%ebp), %edi
@@ -224,11 +223,20 @@ SYM_FUNC_START(startup_32)
        movl    efi32_boot_args+8(%ebp), %edx   // saved bootparams pointer
        cmpl    $0, %edx
        jnz     1f
+       /*
+        * efi_pe_entry uses MS calling convention, which requires 32 bytes of
+        * shadow space on the stack even if all arguments are passed in
+        * registers. We also need an additional 8 bytes for the space that
+        * would be occupied by the return address, and this also results in
+        * the correct stack alignment for entry.
+        */
+       subl    $40, %esp
        leal    efi_pe_entry(%ebp), %eax
        movl    %edi, %ecx                      // MS calling convention
        movl    %esi, %edx
 1:
 #endif
+       pushl   $__KERNEL_CS
        pushl   %eax
 
        /* Enter paged protected Mode, activating Long Mode */
@@ -784,6 +792,7 @@ SYM_DATA_LOCAL(boot_heap,   .fill BOOT_HEAP_SIZE, 1, 0)
 
 SYM_DATA_START_LOCAL(boot_stack)
        .fill BOOT_STACK_SIZE, 1, 0
+       .balign 16
 SYM_DATA_END_LABEL(boot_stack, SYM_L_LOCAL, boot_stack_end)
 
 /*