Skip to content

Commit

Permalink
[elf] Reject ELFBoot images requiring virtual addressing
Browse files Browse the repository at this point in the history 
We do not set up any kind of virtual addressing before invoking an
ELFBoot image.  Reject if the image's program headers indicate that
virtual addresses are not equal to physical addresses.

This avoids problems when loading some RHEL5 kernels, which seem to
include ELFBoot headers using virtual addressing.  With this change,
these kernels are no longer detected as ELFBoot, and so may be
(correctly) detected as bzImage instead.

Reported-by: Torgeir.Wulfsberg@kongsberg.com
Signed-off-by: Michael Brown <mcb30@ipxe.org>
  • Loading branch information
@mcb30
mcb30 committed Jul 29, 2015
1 parent 1e4ff87 commit ae7f22e
Show file tree
Hide file tree
Showing 3 changed files with 131 additions and 52 deletions.
33 changes: 32 additions & 1 deletion src/arch/i386/image/elfboot.c
View file
Expand Up @@ -78,6 +78,27 @@ static int elfboot_exec ( struct image *image ) {
return -ECANCELED; /* -EIMPOSSIBLE, anyone? */
}

/**
* Check that ELF segment uses flat physical addressing
*
* @v image ELF file
* @v phdr ELF program header
* @v dest Destination address
* @ret rc Return status code
*/
static int elfboot_check_segment ( struct image *image, Elf_Phdr *phdr,
physaddr_t dest ) {

/* Check that ELF segment uses flat physical addressing */
if ( phdr->p_vaddr != dest ) {
DBGC ( image, "ELF %p uses virtual addressing (phys %x, "
"virt %x)\n", image, phdr->p_paddr, phdr->p_vaddr );
return -ENOEXEC;
}

return 0;
}

/**
* Probe ELF image
*
Expand All @@ -95,14 +116,24 @@ static int elfboot_probe ( struct image *image ) {
[EI_DATA] = ELFDATA2LSB,
[EI_VERSION] = EV_CURRENT,
};
physaddr_t entry;
physaddr_t max;
int rc;

/* Read ELF header */
copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) );
if ( memcmp ( ehdr.e_ident, e_ident, sizeof ( e_ident ) ) != 0 ) {
DBG ( "Invalid ELF identifier\n" );
DBGC ( image, "Invalid ELF identifier\n" );
return -ENOEXEC;
}

/* Check that this image uses flat physical addressing */
if ( ( rc = elf_segments ( image, &ehdr, elfboot_check_segment,
&entry, &max ) ) != 0 ) {
DBGC ( image, "Unloadable ELF image\n" );
return rc;
}

return 0;
}

Expand Down
139 changes: 88 additions & 51 deletions src/image/elf.c
View file
Expand Up @@ -40,27 +40,54 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <ipxe/image.h>
#include <ipxe/elf.h>

typedef Elf32_Ehdr Elf_Ehdr;
typedef Elf32_Phdr Elf_Phdr;
typedef Elf32_Off Elf_Off;
#define ELFCLASS ELFCLASS32

/**
* Load ELF segment into memory
*
* @v image ELF file
* @v phdr ELF program header
* @v dest Destination address
* @ret rc Return status code
*/
static int elf_load_segment ( struct image *image, Elf_Phdr *phdr,
physaddr_t dest ) {
userptr_t buffer = phys_to_user ( dest );
int rc;

DBGC ( image, "ELF %p loading segment [%x,%x) to [%lx,%lx,%lx)\n",
image, phdr->p_offset, ( phdr->p_offset + phdr->p_filesz ),
dest, ( dest + phdr->p_filesz ), ( dest + phdr->p_memsz ) );

/* Verify and prepare segment */
if ( ( rc = prep_segment ( buffer, phdr->p_filesz,
phdr->p_memsz ) ) != 0 ) {
DBGC ( image, "ELF %p could not prepare segment: %s\n",
image, strerror ( rc ) );
return rc;
}

/* Copy image to segment */
memcpy_user ( buffer, 0, image->data, phdr->p_offset, phdr->p_filesz );

return 0;
}

/**
* Process ELF segment
*
* @v image ELF file
* @v ehdr ELF executable header
* @v phdr ELF program header
* @v process Segment processor
* @ret entry Entry point, if found
* @ret max Maximum used address
* @ret rc Return status code
*/
static int elf_load_segment ( struct image *image, Elf_Phdr *phdr,
Elf_Ehdr *ehdr, physaddr_t *entry,
physaddr_t *max ) {
static int elf_segment ( struct image *image, Elf_Ehdr *ehdr, Elf_Phdr *phdr,
int ( * process ) ( struct image *image,
Elf_Phdr *phdr, physaddr_t dest ),
physaddr_t *entry, physaddr_t *max ) {
physaddr_t dest;
physaddr_t end;
userptr_t buffer;
unsigned long e_offset;
int rc;

Expand All @@ -86,28 +113,15 @@ static int elf_load_segment ( struct image *image, Elf_Phdr *phdr,
image );
return -ENOEXEC;
}
buffer = phys_to_user ( dest );
end = ( dest + phdr->p_memsz );

DBGC ( image, "ELF %p loading segment [%x,%x) to [%x,%x,%x)\n", image,
phdr->p_offset, ( phdr->p_offset + phdr->p_filesz ),
phdr->p_paddr, ( phdr->p_paddr + phdr->p_filesz ),
( phdr->p_paddr + phdr->p_memsz ) );

/* Verify and prepare segment */
if ( ( rc = prep_segment ( buffer, phdr->p_filesz,
phdr->p_memsz ) ) != 0 ) {
DBGC ( image, "ELF %p could not prepare segment: %s\n",
image, strerror ( rc ) );
return rc;
}

/* Update maximum used address, if applicable */
if ( end > *max )
*max = end;

/* Copy image to segment */
memcpy_user ( buffer, 0, image->data, phdr->p_offset, phdr->p_filesz );
/* Process segment */
if ( ( rc = process ( image, phdr, dest ) ) != 0 )
return rc;

/* Set execution address, if it lies within this segment */
if ( ( e_offset = ( ehdr->e_entry - dest ) ) < phdr->p_filesz ) {
Expand All @@ -128,62 +142,85 @@ static int elf_load_segment ( struct image *image, Elf_Phdr *phdr,
}

/**
* Load ELF image into memory
* Process ELF segments
*
* @v image ELF file
* @ret entry Entry point
* @v ehdr ELF executable header
* @v process Segment processor
* @ret entry Entry point, if found
* @ret max Maximum used address
* @ret rc Return status code
*/
int elf_load ( struct image *image, physaddr_t *entry, physaddr_t *max ) {
static const uint8_t e_ident[] = {
[EI_MAG0] = ELFMAG0,
[EI_MAG1] = ELFMAG1,
[EI_MAG2] = ELFMAG2,
[EI_MAG3] = ELFMAG3,
[EI_CLASS] = ELFCLASS,
};
Elf_Ehdr ehdr;
int elf_segments ( struct image *image, Elf_Ehdr *ehdr,
int ( * process ) ( struct image *image, Elf_Phdr *phdr,
physaddr_t dest ),
physaddr_t *entry, physaddr_t *max ) {
Elf_Phdr phdr;
Elf_Off phoff;
unsigned int phnum;
int rc;

/* Read ELF header */
copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) );
if ( memcmp ( &ehdr.e_ident[EI_MAG0], e_ident,
sizeof ( e_ident ) ) != 0 ) {
DBGC ( image, "ELF %p has invalid signature\n", image );
return -ENOEXEC;
}

/* Initialise maximum used address */
*max = 0;

/* Invalidate entry point */
*entry = 0;

/* Read ELF program headers */
for ( phoff = ehdr.e_phoff , phnum = ehdr.e_phnum ; phnum ;
phoff += ehdr.e_phentsize, phnum-- ) {
/* Read and process ELF program headers */
for ( phoff = ehdr->e_phoff , phnum = ehdr->e_phnum ; phnum ;
phoff += ehdr->e_phentsize, phnum-- ) {
if ( phoff > image->len ) {
DBGC ( image, "ELF %p program header %d outside "
"image\n", image, phnum );
return -ENOEXEC;
}
copy_from_user ( &phdr, image->data, phoff, sizeof ( phdr ) );
if ( ( rc = elf_load_segment ( image, &phdr, &ehdr,
entry, max ) ) != 0 ) {
if ( ( rc = elf_segment ( image, ehdr, &phdr, process,
entry, max ) ) != 0 )
return rc;
}
}

/* Check for a valid execution address */
if ( ! *entry ) {
DBGC ( image, "ELF %p entry point %lx outside image\n",
image, ( ( unsigned long ) ehdr.e_entry ) );
image, ( ( unsigned long ) ehdr->e_entry ) );
return -ENOEXEC;
}

return 0;
}

/**
* Load ELF image into memory
*
* @v image ELF file
* @ret entry Entry point
* @ret max Maximum used address
* @ret rc Return status code
*/
int elf_load ( struct image *image, physaddr_t *entry, physaddr_t *max ) {
static const uint8_t e_ident[] = {
[EI_MAG0] = ELFMAG0,
[EI_MAG1] = ELFMAG1,
[EI_MAG2] = ELFMAG2,
[EI_MAG3] = ELFMAG3,
[EI_CLASS] = ELFCLASS,
};
Elf_Ehdr ehdr;
int rc;

/* Read ELF header */
copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) );
if ( memcmp ( &ehdr.e_ident[EI_MAG0], e_ident,
sizeof ( e_ident ) ) != 0 ) {
DBGC ( image, "ELF %p has invalid signature\n", image );
return -ENOEXEC;
}

/* Load ELF segments into memory */
if ( ( rc = elf_segments ( image, &ehdr, elf_load_segment,
entry, max ) ) != 0 )
return rc;

return 0;
}
11 changes: 11 additions & 0 deletions src/include/ipxe/elf.h
View file
Expand Up @@ -10,8 +10,19 @@

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

#include <stdint.h>
#include <ipxe/image.h>
#include <elf.h>

typedef Elf32_Ehdr Elf_Ehdr;
typedef Elf32_Phdr Elf_Phdr;
typedef Elf32_Off Elf_Off;
#define ELFCLASS ELFCLASS32

extern int elf_segments ( struct image *image, Elf_Ehdr *ehdr,
int ( * process ) ( struct image *image,
Elf_Phdr *phdr, physaddr_t dest ),
physaddr_t *entry, physaddr_t *max );
extern int elf_load ( struct image *image, physaddr_t *entry, physaddr_t *max );

#endif /* _IPXE_ELF_H */

0 comments on commit ae7f22e

Please sign in to comment.