mirrors/qemu
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

linux-user: elf: mmap all the target-pages of hostpage for data segment

Browse Source 
If the hostpage size is greater than the TARGET_PAGESIZE, the
target-pages of size TARGET_PAGESIZE are marked valid only till the
length requested during the elfload. The glibc attempts to consume unused
space in the last page of data segment(__libc_memalign() in
elf/dl-minimal.c). If PT_LOAD p_align is greater than or
equal to hostpage size, the GLRO(dl_pagesize) is actually the host pagesize
as set in the auxillary vectors. So, there is no explicit mmap request for
the remaining target-pages on the last hostpage. The glibc assumes that
particular space as available and subsequent attempts to use
those addresses lead to crash as the target_mmap has not marked them valid
for those target-pages.

The issue is seen when trying to chroot to 16.04-x86_64 ubuntu on a PPC64
host where the fork fails to access the thread_id as it is allocated on a
page not marked valid. The recent glibc doesn't have checks for thread-id in
fork, but the issue can manifest somewhere else, none the less.

The fix here is to map all the target-pages of the hostpage during the
elfload if the p_align is greater than or equal to hostpage size, for
data segment to allow the glibc for proper consumption.

Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <153553435604.51992.5640085189104207249.stgit@lep8c.aus.stglabs.ibm.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Shivaprasad G Bhat 2018-08-29 04:23:27 -05:00 committed by Laurent Vivier
parent 83eb6e5090
commit 94894ff2d1
1 changed files with 7 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
linux-user/elfload.c
View File

@ -1437,7 +1437,10 @@ struct exec
#define QMAGIC 0314
/* Necessary parameters */
#define TARGET_ELF_EXEC_PAGESIZE TARGET_PAGE_SIZE
#define TARGET_ELF_EXEC_PAGESIZE \
(((eppnt->p_align & ~qemu_host_page_mask) != 0) ? \
TARGET_PAGE_SIZE : MAX(qemu_host_page_size, TARGET_PAGE_SIZE))
#define TARGET_ELF_PAGELENGTH(_v) ROUND_UP((_v), TARGET_ELF_EXEC_PAGESIZE)
#define TARGET_ELF_PAGESTART(_v) ((_v) & \
~(abi_ulong)(TARGET_ELF_EXEC_PAGESIZE-1))
#define TARGET_ELF_PAGEOFFSET(_v) ((_v) & (TARGET_ELF_EXEC_PAGESIZE-1))
@ -2279,7 +2282,7 @@ static void load_elf_image(const char *image_name, int image_fd,
for (i = 0; i < ehdr->e_phnum; i++) {
struct elf_phdr *eppnt = phdr + i;
if (eppnt->p_type == PT_LOAD) {
abi_ulong vaddr, vaddr_po, vaddr_ps, vaddr_ef, vaddr_em;
abi_ulong vaddr, vaddr_po, vaddr_ps, vaddr_ef, vaddr_em, vaddr_len;
int elf_prot = 0;
if (eppnt->p_flags & PF_R) elf_prot = PROT_READ;
@ -2289,8 +2292,9 @@ static void load_elf_image(const char *image_name, int image_fd,
vaddr = load_bias + eppnt->p_vaddr;
vaddr_po = TARGET_ELF_PAGEOFFSET(vaddr);
vaddr_ps = TARGET_ELF_PAGESTART(vaddr);
vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_filesz + vaddr_po);
error = target_mmap(vaddr_ps, eppnt->p_filesz + vaddr_po,
error = target_mmap(vaddr_ps, vaddr_len,
elf_prot, MAP_PRIVATE | MAP_FIXED,
image_fd, eppnt->p_offset - vaddr_po);
if (error == -1) {