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    SubjectRe: [PATCH v3] binfmt_elf: Fix PIE execution with randomization disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization disabled)
    On Tue, 4 Oct 2011, Jiri Kosina wrote:

    > > Guys, it took several people several days and 10+ emails to work out
    > > what's happening in there, and the first attempt to fix it was buggy.
    > > This is all a huuuuge signal that the code is unobvious, hard to
    > > understand, hard to maintain.
    >
    > It's unfortunately true. Rewriting the ELF binary loader is on my list of
    > very-long-term TODOs. It has became quite a monster over decades.
    >
    > > Please, let's get a good code comment in there while it's fresh in your
    > > minds. So the next person who comes along doesn't have the same amount
    > > of difficulty?

    Andrew,

    find the updated patch below. Please consider applying.

    I believe Cc to stable is appropriate as well.

    Thanks a lot Josh for verification of the fix.



    From: Jiri Kosina <jkosina@suse.cz>
    Subject: [PATCH] binfmt_elf: fix PIE execution with randomization disabled

    The case of address space randomization being disabled in runtime through
    randomize_va_space sysctl is not treated properly in load_elf_binary(),
    resulting in SIGKILL coming at exec() time for certain PIE-linked binaries
    in case the randomization has been disabled at runtime prior to calling
    exec().

    Handle the randomize_va_space == 0 case the same way as if we were not
    supporting .text randomization at all.

    Based on original patch by H.J. Lu <hongjiu.lu@intel.com> and.
    Josh Boyer <jwboyer@redhat.com>

    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Russell King <rmk@arm.linux.org.uk>
    Cc: stable@kernel.org
    Tested-by: Josh Boyer <jwboyer@redhat.com>
    Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
    Signed-off-by: Jiri Kosina <jkosina@suse.cz>
    ---
    fs/binfmt_elf.c | 11 ++++++++++-
    1 files changed, 10 insertions(+), 1 deletions(-)

    diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
    index dd0fdfc..21ac5ee 100644
    --- a/fs/binfmt_elf.c
    +++ b/fs/binfmt_elf.c
    @@ -795,7 +795,16 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
    * might try to exec. This is because the brk will
    * follow the loader, and is not movable. */
    #if defined(CONFIG_X86) || defined(CONFIG_ARM)
    - load_bias = 0;
    + /* Memory randomization might have been switched off
    + * in runtime via sysctl.
    + * If that is the case, retain the original non-zero
    + * load_bias value in order to establish proper
    + * non-randomized mappings.
    + */
    + if (current->flags & PF_RANDOMIZE)
    + load_bias = 0;
    + else
    + load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
    #else
    load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
    #endif
    --
    Jiri Kosina
    SUSE Labs


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