[PATCH v8 19/23] x86/decompressor: Move global symbol references to C code

Ard Biesheuvel
2023-08-02T15:52:06Z

It is no longer necessary to be cautious when referring to global
variables in the position independent decompressor code, now that it is
built using PIE codegen and makes an assertion in the linker script that
no GOT entries exist (which would require adjustment for the actual
runtime load address of the decompressor binary).

This means global variables can be referenced directly from C code,
instead of having to pass their runtime addresses into C routines from
asm code, which needs to happen at each call site. Do so for the code
that will be called directly from the EFI stub after a subsequent patch,
and avoid the need to duplicate this logic a third time.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/head_32.S | 8 --------
arch/x86/boot/compressed/head_64.S | 10 ++--------
arch/x86/boot/compressed/misc.c | 16 +++++++++-------
3 files changed, 11 insertions(+), 23 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 8876ffe30e9a4819..3af4a383615b3e1f 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -168,13 +168,7 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
*/
/* push arguments for extract_kernel: */

- pushl output_len@GOTOFF(%ebx) /* decompressed length, end of relocs */
pushl %ebp /* output address */
- pushl input_len@GOTOFF(%ebx) /* input_len */
- leal input_data@GOTOFF(%ebx), %eax
- pushl %eax /* input_data */
- leal boot_heap@GOTOFF(%ebx), %eax
- pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call extract_kernel /* returns kernel entry point in %eax */
addl $24, %esp
@@ -202,8 +196,6 @@ SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
*/
.bss
.balign 4
-boot_heap:
- .fill BOOT_HEAP_SIZE, 1, 0
boot_stack:
.fill BOOT_STACK_SIZE, 1, 0
boot_stack_end:
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index fb0e562c26f64c9c..28f46051c706724e 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -493,13 +493,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
/*
* Do the extraction, and jump to the new kernel..
*/
- /* pass struct boot_params pointer */
+ /* pass struct boot_params pointer and output target address */
movq %r15, %rdi
- leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
- leaq input_data(%rip), %rdx /* input_data */
- movl input_len(%rip), %ecx /* input_len */
- movq %rbp, %r8 /* output target address */
- movl output_len(%rip), %r9d /* decompressed length, end of relocs */
+ movq %rbp, %rsi
call extract_kernel /* returns kernel entry point in %rax */

/*
@@ -657,8 +653,6 @@ SYM_DATA_END_LABEL(boot_idt, SYM_L_GLOBAL, boot_idt_end)
*/
.bss
.balign 4
-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
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 94b7abcf624b3b55..2d91d56b59e1af93 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -330,6 +330,11 @@ static size_t parse_elf(void *output)
return ehdr.e_entry - LOAD_PHYSICAL_ADDR;
}

+static u8 boot_heap[BOOT_HEAP_SIZE] __aligned(4);
+
+extern unsigned char input_data[];
+extern unsigned int input_len, output_len;
+
/*
* The compressed kernel image (ZO), has been moved so that its position
* is against the end of the buffer used to hold the uncompressed kernel
@@ -347,14 +352,11 @@ static size_t parse_elf(void *output)
* |-------uncompressed kernel image---------|
*
*/
-asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
- unsigned char *input_data,
- unsigned long input_len,
- unsigned char *output,
- unsigned long output_len)
+asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
{
const unsigned long kernel_total_size = VO__end - VO__text;
unsigned long virt_addr = LOAD_PHYSICAL_ADDR;
+ memptr heap = (memptr)boot_heap;
unsigned long needed_size;
size_t entry_offset;

@@ -412,7 +414,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
* entries. This ensures the full mapped area is usable RAM
* and doesn't include any reserved areas.
*/
- needed_size = max(output_len, kernel_total_size);
+ needed_size = max_t(unsigned long, output_len, kernel_total_size);
#ifdef CONFIG_X86_64
needed_size = ALIGN(needed_size, MIN_KERNEL_ALIGN);
#endif
@@ -443,7 +445,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
#ifdef CONFIG_X86_64
if (heap > 0x3fffffffffffUL)
error("Destination address too large");
- if (virt_addr + max(output_len, kernel_total_size) > KERNEL_IMAGE_SIZE)
+ if (virt_addr + needed_size > KERNEL_IMAGE_SIZE)
error("Destination virtual address is beyond the kernel mapping area");
#else
if (heap > ((-__PAGE_OFFSET-(128<<20)-1) & 0x7fffffff))
--
2.39.2