Commit 94894ff2 authored by Shivaprasad G Bhat's avatar Shivaprasad G Bhat Committed by Laurent Vivier
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linux-user: elf: mmap all the target-pages of hostpage for data segment 



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: default avatarShivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
Reviewed-by: default avatarLaurent Vivier <laurent@vivier.eu>
Message-Id: <153553435604.51992.5640085189104207249.stgit@lep8c.aus.stglabs.ibm.com>
Signed-off-by: default avatarLaurent Vivier <laurent@vivier.eu>
parent 83eb6e50

linux-user/elfload.c

+7 −3
Original line number Diff line number Diff line
@@ -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) {