AuxXxilium/linux_dsm_epyc7002
1
0
Fork 0
mirror of https://github.com/AuxXxilium/linux_dsm_epyc7002.git synced 2024-12-16 12:46:55 +07:00
Code Issues Actions Packages Projects Releases Wiki Activity

efi/x86: Don't depend on firmware GDT layout

Browse Source 
When booting in mixed mode, the firmware's GDT is still installed at
handover entry in efi32_stub_entry. We save the GDTR for later use in
__efi64_thunk but we are assuming that descriptor 2 (__KERNEL_CS) is a
valid 32-bit code segment descriptor and that descriptor 3
(__KERNEL_DS/__BOOT_DS) is a valid data segment descriptor.

This happens to be true for OVMF (it actually uses descriptor 1 for data
segments, but descriptor 3 is also setup as data), but we shouldn't
depend on this being the case.

Fix this by saving the code and data selectors in addition to the GDTR
in efi32_stub_entry, and restoring them in __efi64_thunk before calling
the firmware. The UEFI specification guarantees that selectors will be
flat, so using the DS selector for all the segment registers should be
enough.

We also need to install our own GDT before initializing segment
registers in startup_32, so move the GDT load up to the beginning of the
function.

[ardb: mention mixed mode in the commit log]

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200202171353.3736319-3-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Arvind Sankar 2020-02-02 12:13:48 -05:00 committed by Ard Biesheuvel
parent 67a6af7ad1
commit 90ff226281
2 changed files with 42 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
arch/x86/boot/compressed/efi_thunk_64.S
View File

@ -54,11 +54,16 @@ SYM_FUNC_START(__efi64_thunk)
* Switch to gdt with 32-bit segments. This is the firmware GDT
* that was installed when the kernel started executing. This
* pointer was saved at the EFI stub entry point in head_64.S.
*
* Pass the saved DS selector to the 32-bit code, and use far return to
* restore the saved CS selector.
*/
leaq efi32_boot_gdt(%rip), %rax
lgdt (%rax)
pushq $__KERNEL_CS
movzwl efi32_boot_ds(%rip), %edx
movzwq efi32_boot_cs(%rip), %rax
pushq %rax
leaq efi_enter32(%rip), %rax
pushq %rax
lretq
@ -73,6 +78,10 @@ SYM_FUNC_START(__efi64_thunk)
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/* Clear out 32-bit selector from FS and GS */
xorl %ebx, %ebx
movl %ebx, %fs
movl %ebx, %gs
/*
* Convert 32-bit status code into 64-bit.
@ -92,10 +101,12 @@ SYM_FUNC_END(__efi64_thunk)
* The stack should represent the 32-bit calling convention.
*/
SYM_FUNC_START_LOCAL(efi_enter32)
movl $__KERNEL_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
/* Load firmware selector into data and stack segment registers */
movl %edx, %ds
movl %edx, %es
movl %edx, %fs
movl %edx, %gs
movl %edx, %ss
/* Reload pgtables */
movl %cr3, %eax
@ -157,6 +168,14 @@ SYM_DATA_START(efi32_boot_gdt)
.quad 0
SYM_DATA_END(efi32_boot_gdt)
SYM_DATA_START(efi32_boot_cs)
.word 0
SYM_DATA_END(efi32_boot_cs)
SYM_DATA_START(efi32_boot_ds)
.word 0
SYM_DATA_END(efi32_boot_ds)
SYM_DATA_START(efi_gdt64)
.word efi_gdt64_end - efi_gdt64
.long 0 /* Filled out by user */

30
arch/x86/boot/compressed/head_64.S
View File

@ -54,10 +54,6 @@ SYM_FUNC_START(startup_32)
*/
cld
cli
movl $(__BOOT_DS), %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
/*
* Calculate the delta between where we were compiled to run
@ -72,10 +68,20 @@ SYM_FUNC_START(startup_32)
1: popl %ebp
subl $1b, %ebp
/* Load new GDT with the 64bit segments using 32bit descriptor */
addl %ebp, gdt+2(%ebp)
lgdt gdt(%ebp)
/* Load segment registers with our descriptors */
movl $__BOOT_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %fs
movl %eax, %gs
movl %eax, %ss
/* setup a stack and make sure cpu supports long mode. */
movl $boot_stack_end, %eax
addl %ebp, %eax
movl %eax, %esp
leal boot_stack_end(%ebp), %esp
call verify_cpu
testl %eax, %eax
@ -112,10 +118,6 @@ SYM_FUNC_START(startup_32)
* Prepare for entering 64 bit mode
*/
/* Load new GDT with the 64bit segments using 32bit descriptor */
addl %ebp, gdt+2(%ebp)
lgdt gdt(%ebp)
/* Enable PAE mode */
movl %cr4, %eax
orl $X86_CR4_PAE, %eax
@ -232,9 +234,13 @@ SYM_FUNC_START(efi32_stub_entry)
movl %ecx, efi32_boot_args(%ebp)
movl %edx, efi32_boot_args+4(%ebp)
sgdtl efi32_boot_gdt(%ebp)
movb $0, efi_is64(%ebp)
/* Save firmware GDTR and code/data selectors */
sgdtl efi32_boot_gdt(%ebp)
movw %cs, efi32_boot_cs(%ebp)
movw %ds, efi32_boot_ds(%ebp)
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax