diff options
| author | Arvind Sankar <nivedita@alum.mit.edu> | 2020-10-29 12:19:03 -0400 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2020-10-29 21:54:35 +0100 |
| commit | ea3186b9572a1b0299448697cfc44920061872cf (patch) | |
| tree | 82474a7fd03a53c744ee9c491b4018c96eda4c63 /arch/x86/include/asm/page_32_types.h | |
| parent | 3650b228f83adda7e5ee532e2b90429c03f7b9ec (diff) | |
x86/build: Fix vmlinux size check on 64-bit
Commit
b4e0409a36f4 ("x86: check vmlinux limits, 64-bit")
added a check that the size of the 64-bit kernel is less than
KERNEL_IMAGE_SIZE.
The check uses (_end - _text), but this is not enough. The initial
PMD used in startup_64() (level2_kernel_pgt) can only map upto
KERNEL_IMAGE_SIZE from __START_KERNEL_map, not from _text, and the
modules area (MODULES_VADDR) starts at KERNEL_IMAGE_SIZE.
The correct check is what is currently done for 32-bit, since
LOAD_OFFSET is defined appropriately for the two architectures. Just
check (_end - LOAD_OFFSET) against KERNEL_IMAGE_SIZE unconditionally.
Note that on 32-bit, the limit is not strict: KERNEL_IMAGE_SIZE is not
really used by the main kernel. The higher the kernel is located, the
less the space available for the vmalloc area. However, it is used by
KASLR in the compressed stub to limit the maximum address of the kernel
to a safe value.
Clean up various comments to clarify that despite the name,
KERNEL_IMAGE_SIZE is not a limit on the size of the kernel image, but a
limit on the maximum virtual address that the image can occupy.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201029161903.2553528-1-nivedita@alum.mit.edu
Diffstat (limited to 'arch/x86/include/asm/page_32_types.h')
| -rw-r--r-- | arch/x86/include/asm/page_32_types.h | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h index f462895a33e4..faf9cc1c14bb 100644 --- a/arch/x86/include/asm/page_32_types.h +++ b/arch/x86/include/asm/page_32_types.h @@ -53,7 +53,13 @@ #define STACK_TOP_MAX STACK_TOP /* - * Kernel image size is limited to 512 MB (see in arch/x86/kernel/head_32.S) + * In spite of the name, KERNEL_IMAGE_SIZE is a limit on the maximum virtual + * address for the kernel image, rather than the limit on the size itself. On + * 32-bit, this is not a strict limit, but this value is used to limit the + * link-time virtual address range of the kernel, and by KASLR to limit the + * randomized address from which the kernel is executed. A relocatable kernel + * can be loaded somewhat higher than KERNEL_IMAGE_SIZE as long as enough space + * remains for the vmalloc area. */ #define KERNEL_IMAGE_SIZE (512 * 1024 * 1024) |