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[elf] Work around entry point bug in NetBSD kernels 

NetBSD kernels are multiboot ELF kernels with an entry point
incorrectly specified as a virtual address rather than a physical
address.

Work around this by looking for the segment that could plausibly
contain the entry point address (interpreted as either a physical or
virtual address), and using that to determine the eventual physical
entry point.

In the event of any ambiguity, precedence is given to interpretation
of the entry point as a physical address.
pull/1/head
Michael Brown 2009-04-24 03:42:34 +01:00
parent e960fac8d0
commit 4b8e021161
1 changed files with 41 additions and 14 deletions
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55
src/image/elf.c
View File

@ -42,11 +42,14 @@ typedef Elf32_Off Elf_Off;
* *
* @v image ELF file * @v image ELF file
* @v phdr ELF program header * @v phdr ELF program header
* @v ehdr ELF executable header
* @ret rc Return status code * @ret rc Return status code
*/ */
static int elf_load_segment ( struct image *image, Elf_Phdr *phdr ) { static int elf_load_segment ( struct image *image, Elf_Phdr *phdr,
Elf_Ehdr *ehdr ) {
physaddr_t dest; physaddr_t dest;
userptr_t buffer; userptr_t buffer;
unsigned long e_offset;
int rc; int rc;
/* Do nothing for non-PT_LOAD segments */ /* Do nothing for non-PT_LOAD segments */
@ -55,7 +58,7 @@ static int elf_load_segment ( struct image *image, Elf_Phdr *phdr ) {
/* Check segment lies within image */ /* Check segment lies within image */
if ( ( phdr->p_offset + phdr->p_filesz ) > image->len ) { if ( ( phdr->p_offset + phdr->p_filesz ) > image->len ) {
DBG ( "ELF segment outside ELF file\n" ); DBGC ( image, "ELF %p segment outside image\n", image );
return -ENOEXEC; return -ENOEXEC;
} }
@ -67,26 +70,43 @@ static int elf_load_segment ( struct image *image, Elf_Phdr *phdr ) {
if ( ! dest ) if ( ! dest )
dest = phdr->p_vaddr; dest = phdr->p_vaddr;
if ( ! dest ) { if ( ! dest ) {
DBG ( "ELF segment loads to physical address 0\n" ); DBGC ( image, "ELF %p segment loads to physical address 0\n",
image );
return -ENOEXEC; return -ENOEXEC;
} }
buffer = phys_to_user ( dest ); buffer = phys_to_user ( dest );
DBG ( "ELF loading segment [%x,%x) to [%x,%x,%x)\n", 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_offset, ( phdr->p_offset + phdr->p_filesz ),
phdr->p_paddr, ( phdr->p_paddr + phdr->p_filesz ), phdr->p_paddr, ( phdr->p_paddr + phdr->p_filesz ),
( phdr->p_paddr + phdr->p_memsz ) ); ( phdr->p_paddr + phdr->p_memsz ) );
/* Verify and prepare segment */ /* Verify and prepare segment */
if ( ( rc = prep_segment ( buffer, phdr->p_filesz, if ( ( rc = prep_segment ( buffer, phdr->p_filesz,
phdr->p_memsz ) ) != 0 ) { phdr->p_memsz ) ) != 0 ) {
DBG ( "ELF could not prepare segment: %s\n", strerror ( rc ) ); DBGC ( image, "ELF %p could not prepare segment: %s\n",
image, strerror ( rc ) );
return rc; return rc;
} }
/* Copy image to segment */ /* Copy image to segment */
memcpy_user ( buffer, 0, image->data, phdr->p_offset, phdr->p_filesz ); memcpy_user ( buffer, 0, image->data, phdr->p_offset, phdr->p_filesz );
/* Set execution address, if it lies within this segment */
if ( ( e_offset = ( ehdr->e_entry - dest ) ) < phdr->p_filesz ) {
image->priv.phys = ehdr->e_entry;
DBGC ( image, "ELF %p found physical entry point at %lx\n",
image, image->priv.phys );
} else if ( ( e_offset = ( ehdr->e_entry - phdr->p_vaddr ) )
< phdr->p_filesz ) {
if ( ! image->priv.phys ) {
image->priv.phys = ( dest + e_offset );
DBGC ( image, "ELF %p found virtual entry point at %lx"
" (virt %lx)\n", image, image->priv.phys,
( ( unsigned long ) ehdr->e_entry ) );
}
}
return 0; return 0;
} }
@ -109,25 +129,32 @@ int elf_load ( struct image *image ) {
/* Read ELF header */ /* Read ELF header */
copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) ); copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) );
if ( memcmp ( &ehdr.e_ident[EI_MAG0], ELFMAG, SELFMAG ) != 0 ) { if ( memcmp ( &ehdr.e_ident[EI_MAG0], ELFMAG, SELFMAG ) != 0 ) {
DBG ( "Invalid ELF signature\n" ); DBGC ( image, "ELF %p has invalid signature\n", image );
return -ENOEXEC; return -ENOEXEC;
} }
/* Invalidate execution address */
image->priv.phys = 0;
/* Read ELF program headers */ /* Read ELF program headers */
for ( phoff = ehdr.e_phoff , phnum = ehdr.e_phnum ; phnum ; for ( phoff = ehdr.e_phoff , phnum = ehdr.e_phnum ; phnum ;
phoff += ehdr.e_phentsize, phnum-- ) { phoff += ehdr.e_phentsize, phnum-- ) {
if ( phoff > image->len ) { if ( phoff > image->len ) {
DBG ( "ELF program header %d outside ELF image\n", DBGC ( image, "ELF %p program header %d outside "
phnum ); "image\n", image, phnum );
return -ENOEXEC; return -ENOEXEC;
} }
copy_from_user ( &phdr, image->data, phoff, sizeof ( phdr ) ); copy_from_user ( &phdr, image->data, phoff, sizeof ( phdr ) );
if ( ( rc = elf_load_segment ( image, &phdr ) ) != 0 ) if ( ( rc = elf_load_segment ( image, &phdr, &ehdr ) ) != 0 )
return rc; return rc;
} }
/* Record execution entry point in image private data field */ /* Check for a valid execution address */
image->priv.phys = ehdr.e_entry; if ( ! image->priv.phys ) {
DBGC ( image, "ELF %p entry point %lx outside image\n",
image, ( ( unsigned long ) ehdr.e_entry ) );
return -ENOEXEC;
}
return 0; return 0;
} }