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Subject[PATCH 16/28] efi/x86: Decompress at start of PE image load address
Date
From: Arvind Sankar <nivedita@alum.mit.edu>

When booted via PE loader, define image_offset to hold the offset of
startup_32 from the start of the PE image, and use it as the start of
the decompression buffer.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200303221205.4048668-3-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/head_32.S | 17 ++++++++++
arch/x86/boot/compressed/head_64.S | 42 +++++++++++++++++++++++--
drivers/firmware/efi/libstub/x86-stub.c | 17 ++++++++--
3 files changed, 70 insertions(+), 6 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 2a8965aec234..f7b52ccaa4ee 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -100,6 +100,19 @@ SYM_FUNC_START(startup_32)

#ifdef CONFIG_RELOCATABLE
movl %edx, %ebx
+
+#ifdef CONFIG_EFI_STUB
+/*
+ * If we were loaded via the EFI LoadImage service, startup_32 will be at an
+ * offset to the start of the space allocated for the image. efi_pe_entry will
+ * setup image_offset to tell us where the image actually starts, so that we
+ * can use the full available buffer.
+ * image_offset = startup_32 - image_base
+ * Otherwise image_offset will be zero and have no effect on the calculations.
+ */
+ subl image_offset(%edx), %ebx
+#endif
+
movl BP_kernel_alignment(%esi), %eax
decl %eax
addl %eax, %ebx
@@ -227,6 +240,10 @@ SYM_DATA_START_LOCAL(gdt)
.quad 0x00cf92000000ffff /* __KERNEL_DS */
SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)

+#ifdef CONFIG_EFI_STUB
+SYM_DATA(image_offset, .long 0)
+#endif
+
/*
* Stack and heap for uncompression
*/
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 1199c4ef0c83..4d4b4763a770 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -99,6 +99,19 @@ SYM_FUNC_START(startup_32)

#ifdef CONFIG_RELOCATABLE
movl %ebp, %ebx
+
+#ifdef CONFIG_EFI_STUB
+/*
+ * If we were loaded via the EFI LoadImage service, startup_32 will be at an
+ * offset to the start of the space allocated for the image. efi_pe_entry will
+ * setup image_offset to tell us where the image actually starts, so that we
+ * can use the full available buffer.
+ * image_offset = startup_32 - image_base
+ * Otherwise image_offset will be zero and have no effect on the calculations.
+ */
+ subl image_offset(%ebp), %ebx
+#endif
+
movl BP_kernel_alignment(%esi), %eax
decl %eax
addl %eax, %ebx
@@ -111,9 +124,8 @@ SYM_FUNC_START(startup_32)
1:

/* Target address to relocate to for decompression */
- movl BP_init_size(%esi), %eax
- subl $_end, %eax
- addl %eax, %ebx
+ addl BP_init_size(%esi), %ebx
+ subl $_end, %ebx

/*
* Prepare for entering 64 bit mode
@@ -299,6 +311,20 @@ SYM_CODE_START(startup_64)
/* Start with the delta to where the kernel will run at. */
#ifdef CONFIG_RELOCATABLE
leaq startup_32(%rip) /* - $startup_32 */, %rbp
+
+#ifdef CONFIG_EFI_STUB
+/*
+ * If we were loaded via the EFI LoadImage service, startup_32 will be at an
+ * offset to the start of the space allocated for the image. efi_pe_entry will
+ * setup image_offset to tell us where the image actually starts, so that we
+ * can use the full available buffer.
+ * image_offset = startup_32 - image_base
+ * Otherwise image_offset will be zero and have no effect on the calculations.
+ */
+ movl image_offset(%rip), %eax
+ subq %rax, %rbp
+#endif
+
movl BP_kernel_alignment(%rsi), %eax
decl %eax
addq %rax, %rbp
@@ -647,6 +673,10 @@ SYM_DATA_START_LOCAL(gdt)
.quad 0x0000000000000000 /* TS continued */
SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)

+#ifdef CONFIG_EFI_STUB
+SYM_DATA(image_offset, .long 0)
+#endif
+
#ifdef CONFIG_EFI_MIXED
SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0, 0)
SYM_DATA(efi_is64, .byte 1)
@@ -712,6 +742,12 @@ SYM_FUNC_START(efi32_pe_entry)
movl -4(%ebp), %esi // loaded_image
movl LI32_image_base(%esi), %esi // loaded_image->image_base
movl %ebx, %ebp // startup_32 for efi32_pe_stub_entry
+ /*
+ * We need to set the image_offset variable here since startup_32 will
+ * use it before we get to the 64-bit efi_pe_entry in C code.
+ */
+ subl %esi, %ebx
+ movl %ebx, image_offset(%ebp) // save image_offset
jmp efi32_pe_stub_entry

2: popl %edi // restore callee-save registers
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 69a942f0640b..96bc4a8733c8 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -19,6 +19,7 @@

static efi_system_table_t *sys_table;
extern const bool efi_is64;
+extern u32 image_offset;

__pure efi_system_table_t *efi_system_table(void)
{
@@ -365,6 +366,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
struct boot_params *boot_params;
struct setup_header *hdr;
efi_loaded_image_t *image;
+ void *image_base;
efi_guid_t proto = LOADED_IMAGE_PROTOCOL_GUID;
int options_size = 0;
efi_status_t status;
@@ -385,7 +387,10 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
efi_exit(handle, status);
}

- hdr = &((struct boot_params *)efi_table_attr(image, image_base))->hdr;
+ image_base = efi_table_attr(image, image_base);
+ image_offset = (void *)startup_32 - image_base;
+
+ hdr = &((struct boot_params *)image_base)->hdr;
above4g = hdr->xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G;

status = efi_allocate_pages(0x4000, (unsigned long *)&boot_params,
@@ -400,7 +405,7 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
hdr = &boot_params->hdr;

/* Copy the second sector to boot_params */
- memcpy(&hdr->jump, efi_table_attr(image, image_base) + 512, 512);
+ memcpy(&hdr->jump, image_base + 512, 512);

/*
* Fill out some of the header fields ourselves because the
@@ -727,7 +732,7 @@ unsigned long efi_main(efi_handle_t handle,
* If the kernel isn't already loaded at the preferred load
* address, relocate it.
*/
- if (bzimage_addr != hdr->pref_address) {
+ if (bzimage_addr - image_offset != hdr->pref_address) {
status = efi_relocate_kernel(&bzimage_addr,
hdr->init_size, hdr->init_size,
hdr->pref_address,
@@ -737,6 +742,12 @@ unsigned long efi_main(efi_handle_t handle,
efi_printk("efi_relocate_kernel() failed!\n");
goto fail;
}
+ /*
+ * Now that we've copied the kernel elsewhere, we no longer
+ * have a setup block before startup_32, so reset image_offset
+ * to zero in case it was set earlier.
+ */
+ image_offset = 0;
}

/*
--
2.17.1
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