On 2023-03-09 19:00, Ard Biesheuvel wrote:
On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@xxxxxxxxx> wrote:
Doing it that way allows setting up stricter memory attributes,
simplifies boot code path and removes potential relocation
of kernel image.
Wire up required interfaces and minimally initialize zero page
fields needed for it to function correctly.
Tested-by: Peter Jones <pjones@xxxxxxxxxx>
Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
---
arch/x86/boot/compressed/head_32.S | 50 ++++-
arch/x86/boot/compressed/head_64.S | 58 ++++-
drivers/firmware/efi/Kconfig | 2 +
drivers/firmware/efi/libstub/Makefile | 2 +-
.../firmware/efi/libstub/x86-extract-direct.c | 208
++++++++++++++++++
drivers/firmware/efi/libstub/x86-stub.c | 119 +---------
drivers/firmware/efi/libstub/x86-stub.h | 14 ++
7 files changed, 338 insertions(+), 115 deletions(-)
create mode 100644 drivers/firmware/efi/libstub/x86-extract-direct.c
create mode 100644 drivers/firmware/efi/libstub/x86-stub.h
diff --git a/arch/x86/boot/compressed/head_32.S
b/arch/x86/boot/compressed/head_32.S
index ead6007df1e5..0be75e5072ae 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -152,11 +152,57 @@ SYM_FUNC_END(startup_32)
#ifdef CONFIG_EFI_STUB
SYM_FUNC_START(efi32_stub_entry)
+/*
+ * Calculate the delta between where we were compiled to run
+ * at and where we were actually loaded at. This can only be done
+ * with a short local call on x86. Nothing else will tell us what
+ * address we are running at. The reserved chunk of the real-mode
+ * data at 0x1e4 (defined as a scratch field) are used as the stack
+ * for this calculation. Only 4 bytes are needed.
+ */
Please drop this comment
Will do.
+ call 1f
+1: popl %ebx
+ addl $_GLOBAL_OFFSET_TABLE_+(.-1b), %ebx
Please drop this and ...
+
+ /* Clear BSS */
+ xorl %eax, %eax
+ leal _bss@GOTOFF(%ebx), %edi
+ leal _ebss@GOTOFF(%ebx), %ecx
just use (_bss - 1b) here (etc)
I was trying to be consistent with the code below, but it will
indeed be better to do this like that. I guess, this will be
fine to stop putting GOT address to the %ebx, since the extraction
code does not use calls via PLT?
+ subl %edi, %ecx
+ shrl $2, %ecx
+ rep stosl
+
add $0x4, %esp
movl 8(%esp), %esi /* save boot_params pointer */
+ movl %edx, %edi /* save GOT address */
What does this do?
Hmm... It seems to be a remnant of the previous implementation
that I forgot to remove. I will remove that in the v5.
call efi_main
- /* efi_main returns the possibly relocated address of
startup_32 */
- jmp *%eax
+ movl %eax, %ecx
+
+ /*
+ * efi_main returns the possibly
+ * relocated address of extracted kernel entry point.
+ */
+
+ cli
+
+ /* Load new GDT */
+ leal gdt@GOTOFF(%ebx), %eax
+ movl %eax, 2(%eax)
+ lgdt (%eax)
+
+ /* 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
+
+ /* Zero EFLAGS */
+ pushl $0
+ popfl
+
+ jmp *%ecx
SYM_FUNC_END(efi32_stub_entry)
SYM_FUNC_ALIAS(efi_stub_entry, efi32_stub_entry)
#endif
...
Thanks,
Evgeniy Baskov
