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boot/stub: honor PE SectionAlignment when loading inner kernel

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The stub copies the embedded kernel PE into an xmalloc_pages()
allocation with AllocateAnyPages, which only guarantees EFI_PAGE_SIZE
(4 KiB) alignment.

The arm64 kernel declares SectionAlignment = SZ_64K. When _text is not
64K-aligned the kernel's EFI stub reallocates and copies the image,
which can fail with EFI_OUT_OF_RESOURCES on memory-constrained firmware
(e.g. U-Boot, bounded by CONFIG_SYS_MALLOC_LEN rather than full DRAM).
The failure is non-deterministic since AllocateAnyPages returns whatever
page the allocator finds first.

Plumb SectionAlignment through pe_kernel_info() and allocate via
xmalloc_aligned_pages(). For alignment <= EFI_PAGE_SIZE (e.g. x86_64) it
reduces to a plain AllocatePages(), so the change is free there.

SectionAlignment comes from the PE header, which the spec requires to be
a power of 2. Sanitize it in pe_kernel_info() right where it is parsed:
a non-conforming value falls back to plain page alignment (matching the
behavior of older systemd-stub versions that ignored the field) rather
than propagate something that would break xmalloc_aligned_pages()'s
over-alignment maths, with a log_warning() so the fallback stays
diagnosable.

Co-developed-by: Claude <claude@anthropic.com>

Closes: #42443
Reported-By: Agathe Porte <agathe.porte@oss.qualcomm.com>
Tested-By: Agathe Porte <agathe.porte@oss.qualcomm.com>
This commit is contained in:
Josh Hoffer
2026-06-19 22:16:28 +02:00
committed by Lennart Poettering
parent 347f35cf42
commit e641f37499
4 changed files with 41 additions and 8 deletions
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src/boot/linux.c
+13 -5
View File
@@ -160,14 +160,14 @@ EFI_STATUS linux_exec(
const struct iovec *initrd) {
size_t kernel_size_in_memory = 0;
uint32_t compat_entry_point, entry_point;
uint32_t compat_entry_point, entry_point, section_alignment;
EFI_STATUS err;
assert(parent_image);
assert(iovec_is_set(kernel));
assert(iovec_is_valid(initrd));
err = pe_kernel_info(kernel->iov_base, &entry_point, &compat_entry_point, &kernel_size_in_memory);
err = pe_kernel_info(kernel->iov_base, &entry_point, &compat_entry_point, &kernel_size_in_memory, &section_alignment);
#if defined(__i386__) || defined(__x86_64__)
if (err == EFI_UNSUPPORTED)
/* Kernel is too old to support LINUX_INITRD_MEDIA_GUID, try the deprecated EFI handover
@@ -264,9 +264,17 @@ EFI_STATUS linux_exec(
if (err != EFI_SUCCESS)
return log_error_status(err, "Cannot read sections: %m");
/* Do we need to ensure under 4gb address on x86? */
_cleanup_pages_ Pages loaded_kernel_pages = xmalloc_pages(
AllocateAnyPages, EfiLoaderCode, EFI_SIZE_TO_PAGES(kernel_size_in_memory), 0);
/* Honor the PE SectionAlignment (SZ_64K on arm64): if _text is not aligned the kernel's EFI stub
* reallocates and copies the image, which can fail with EFI_OUT_OF_RESOURCES on memory-constrained
* firmware. When alignment <= EFI_PAGE_SIZE (e.g. x86_64) xmalloc_aligned_pages() reduces to a
* plain AllocatePages() with no extra over-allocation. pe_kernel_info() already sanitized a
* non-conforming SectionAlignment to plain page alignment. */
_cleanup_pages_ Pages loaded_kernel_pages = xmalloc_aligned_pages(
AllocateAnyPages,
EfiLoaderCode,
EFI_SIZE_TO_PAGES(kernel_size_in_memory),
section_alignment,
/* addr= */ 0);
uint8_t* loaded_kernel = PHYSICAL_ADDRESS_TO_POINTER(loaded_kernel_pages.addr);
FOREACH_ARRAY(h, headers, n_headers) {