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    Subject[PATCH v2] binfmt_elf: Fix PIE execution with randomization disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization disabled)
    On Mon, 3 Oct 2011, Josh Boyer wrote:

    > > > Perhaps another check here for randomize? Something like:
    > > >
    > > > #if defined(CONFIG_X86) || defined(CONFIG_ARM)
    > > > if (current->flags & PF_RANDOMIZE)
    > > > load_bias = 0;
    > > > else if (vaddr)
    > > > load_bias = 0;
    > > > else
    > > > load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE);
    > > > #else
    > > > load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
    > > > #endif
    > > >
    > > > If that's stupid, then feel free to tell me. I won't pretend like I
    > > > understand what is going on here yet, but based on the explanation you
    > > > provided that might work.
    > >
    > > I have just verified my hunch that the original patch from H.J. / Josh
    > > breaks ASLR completely, so Andrew, please drop it for now.
    >
    > Yes, please drop the original.

    Thanks.

    > > I am now looking into how to fix things properly.
    > >
    > > Josh, looking at what you are proposing -- do you see any reason to make
    > > the behavior different in #else branch and in !(current->flags &
    > > PF_RANDOMIZE) case?
    >
    > I was mostly just trying to adapt H.J.'s patch to account for the
    > PF_RANDOMIZE case. Looking at it a bit more, I'm not sure why they
    > would need to be different. H.J., do you recall why you made that
    > change originally?

    How about the patch below instead? It survives my testing, and I believe
    it handles both cases properly.

    Confirmation from the original bug reporter would obviously be a nice
    bonus too :)




    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: Jiri Kosina <jkosina@suse.cz>
    Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
    Cc: Russell King <rmk@arm.linux.org.uk>
    Signed-off-by: Jiri Kosina <jkosina@suse.cz>
    ---
    fs/binfmt_elf.c | 5 ++++-
    1 files changed, 4 insertions(+), 1 deletions(-)

    diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
    index dd0fdfc..bb11fe4 100644
    --- a/fs/binfmt_elf.c
    +++ b/fs/binfmt_elf.c
    @@ -795,7 +795,10 @@ 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;
    + 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


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