From: Arvind Sankar <nivedita@alum.mit.edu>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi <linux-efi@vger.kernel.org>, X86 ML <x86@kernel.org>
Subject: [PATCH v2] efi/x86: Setup stack correctly for efi_pe_entry
Date: Wed, 17 Jun 2020 09:19:57 -0400 [thread overview]
Message-ID: <20200617131957.2507632-1-nivedita@alum.mit.edu> (raw)
In-Reply-To: <CAMj1kXGovNeVTm3sSwpk6Lqk=JkBq_gV0t3WKd1=kJ11+C2e5g@mail.gmail.com>
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.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/compressed/head_64.S | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index e821a7d7d5c4..97d37f0a34f5 100644
--- 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)
/*
--
2.26.2
next prev parent reply other threads:[~2020-06-17 13:20 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-26 17:02 [PATCH 0/1] efi/x86: Use firmware stack for mixed-mode EFI stub Arvind Sankar
2020-05-26 17:02 ` [PATCH 1/1] " Arvind Sankar
2020-06-15 9:58 ` Ard Biesheuvel
2020-06-15 15:56 ` Arvind Sankar
2020-06-16 18:48 ` Arvind Sankar
2020-06-16 18:50 ` Ard Biesheuvel
2020-06-16 19:48 ` [PATCH] efi/x86: Setup stack correctly for efi_pe_entry Arvind Sankar
2020-06-16 22:06 ` Ard Biesheuvel
2020-06-17 10:33 ` Ard Biesheuvel
2020-06-17 13:19 ` Arvind Sankar [this message]
2020-06-17 13:26 ` [PATCH v2] " Ard Biesheuvel
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