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loader: Verify alignment of the LOAD segment for the x86-64 kernel #227

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14 changes: 7 additions & 7 deletions docs/elfio_files/bad_align_writer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -56,10 +56,10 @@ int main( void )
// Create a loadable segment
segment* text_seg = writer.segments.add();
text_seg->set_type( PT_LOAD );
text_seg->set_virtual_address( 0x400 );
text_seg->set_physical_address( 0x400 );
text_seg->set_virtual_address( 0x200000 );
text_seg->set_physical_address( 0x200000 );
text_seg->set_flags( PF_X | PF_R );
text_seg->set_align( 0x100 );
text_seg->set_align( 0x200000 );

// Add code section into program segment
text_seg->add_section_index( text_sec->get_index(),
Expand All @@ -80,10 +80,10 @@ int main( void )
// Create a read/write segment
segment* data_seg = writer.segments.add();
data_seg->set_type( PT_NOTE );
data_seg->set_virtual_address( 0x8888048020 );
data_seg->set_physical_address( 0x8888048020 );
data_seg->set_virtual_address( 0x8888400000 );
data_seg->set_physical_address( 0x888400000 );
data_seg->set_flags( PF_W | PF_R );
data_seg->set_align( 13 );
data_seg->set_align( 0x200000 );

// Add code section into program segment
data_seg->add_section_index( data_sec->get_index(),
Expand All @@ -103,7 +103,7 @@ int main( void )
// In this example, the code starts at the first address of the
// 'text_seg' segment. Therefore, the start address is set
// to be equal to the segment location
writer.set_entry( 0x400 );
writer.set_entry( 0x200000 );

// Create ELF file
writer.save( "test_bad_align.bin" );
Expand Down
14 changes: 7 additions & 7 deletions docs/elfio_files/basic_elf.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -56,10 +56,10 @@ int main( void )
// Create a loadable segment
segment* text_seg = writer.segments.add();
text_seg->set_type( PT_LOAD );
text_seg->set_virtual_address( 0x400 );
text_seg->set_physical_address( 0x0 );
text_seg->set_virtual_address( 0x200000 );
text_seg->set_physical_address( 0x200000 );
text_seg->set_flags( PF_X | PF_R );
text_seg->set_align( 0x1 );
text_seg->set_align( 0x200000 );

// Add code section into program segment
text_seg->add_section_index( text_sec->get_index(),
Expand All @@ -80,10 +80,10 @@ int main( void )
// Create a read/write segment
segment* data_seg = writer.segments.add();
data_seg->set_type( PT_LOAD );
data_seg->set_virtual_address( 0x0420 );
data_seg->set_physical_address( 0x0420 );
data_seg->set_virtual_address( 0x400000 );
data_seg->set_physical_address( 0x400000 );
data_seg->set_flags( PF_W | PF_R );
data_seg->set_align( 0x10 );
data_seg->set_align( 0x200000 );

// Add code section into program segment
data_seg->add_section_index( data_sec->get_index(),
Expand All @@ -103,7 +103,7 @@ int main( void )
// In this example, the code starts at the first address of the
// 'text_seg' segment. Therefore, the start address is set
// to be equal to the segment location
writer.set_entry( 0x400 );
writer.set_entry( 0x200000 );

// Create ELF file
writer.save( "test_elf.bin" );
Expand Down
45 changes: 38 additions & 7 deletions src/loader/elf/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -135,6 +135,9 @@ impl fmt::Display for PvhBootCapability {
/// Raw ELF (a.k.a. vmlinux) kernel image support.
pub struct Elf;

// x86-64 kernel must be aligned to 2MB.
const KERNEL_SEGMENT_ALIGN: u64 = 0x200000; // 2 MiB

impl Elf {
/// Verifies that magic numbers are present in the Elf header.
fn validate_header(ehdr: &elf::Elf64_Ehdr) -> std::result::Result<(), Error> {
Expand Down Expand Up @@ -224,12 +227,18 @@ impl KernelLoader for Elf {

let mut loader_result = KernelLoaderResult {
kernel_load: match kernel_offset {
Some(k_offset) => GuestAddress(
k_offset
Some(k_offset) => {
let load_addr = k_offset
.raw_value()
.checked_add(ehdr.e_entry)
.ok_or(Error::Overflow)?,
),
.ok_or(Error::Overflow)?;
// Ensure that kernel_offset is aligned to 2M, otherwise, the kernel may hang during
// booting. Refer to the check in __startup_64() in the Linux kernel source code.
if k_offset.raw_value() & (KERNEL_SEGMENT_ALIGN - 1) != 0 {
return Err(Error::Align.into());
}
GuestAddress(load_addr)
},
None => GuestAddress(ehdr.e_entry),
},
..Default::default()
Expand Down Expand Up @@ -271,6 +280,12 @@ impl KernelLoader for Elf {
.seek(SeekFrom::Start(phdr.p_offset))
.map_err(|_| Error::SeekKernelStart)?;

// Verify alignment of the LOAD segment.
// See commit c55b8550fa57ba4f5e507be406ff9fc2845713e8 in Linux kernel tree.
if phdr.p_align & (KERNEL_SEGMENT_ALIGN - 1) != 0 {
return Err(Error::Align.into());
}

// if the vmm does not specify where the kernel should be loaded, just
// load it to the physical address p_paddr for each segment.
let mem_offset = match kernel_offset {
Expand Down Expand Up @@ -479,10 +494,10 @@ mod tests {
Some(highmem_start_address),
)
.unwrap();
assert_eq!(loader_result.kernel_load.raw_value(), 0x200400);
assert_eq!(loader_result.kernel_load.raw_value(), 0x400000);

loader_result = Elf::load(&gm, Some(kernel_addr), &mut Cursor::new(&image), None).unwrap();
assert_eq!(loader_result.kernel_load.raw_value(), 0x200400);
assert_eq!(loader_result.kernel_load.raw_value(), 0x400000);

loader_result = Elf::load(
&gm,
Expand All @@ -491,7 +506,7 @@ mod tests {
Some(highmem_start_address),
)
.unwrap();
assert_eq!(loader_result.kernel_load.raw_value(), 0x400);
assert_eq!(loader_result.kernel_load.raw_value(), 0x200000);

highmem_start_address = GuestAddress(0xa00000);
assert_eq!(
Expand Down Expand Up @@ -632,4 +647,20 @@ mod tests {
.err()
);
}

#[test]
fn test_unaligned_loadaddr() {
let gm = create_guest_mem();
let image = make_elf_bin();
assert_eq!(
Some(KernelLoaderError::Elf(Error::Align)),
Elf::load(
&gm,
Some(GuestAddress(0x1000)),
&mut Cursor::new(&image),
None
)
.err()
);
}
}
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