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On Mon, 3 Oct 2011, Josh Boyer wrote:
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> > > Perhaps another check here for randomize? Something like:
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> > >
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> > > #if defined(CONFIG_X86) || defined(CONFIG_ARM)
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> > > if (current->flags & PF_RANDOMIZE)
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> > > load_bias = 0;
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> > > else if (vaddr)
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> > > load_bias = 0;
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> > > else
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> > > load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE);
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> > > #else
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> > > load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
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> > > #endif
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> > >
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> > > If that's stupid, then feel free to tell me. I won't pretend like I
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> > > understand what is going on here yet, but based on the explanation you
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> > > provided that might work.
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> >
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> > I have just verified my hunch that the original patch from H.J. / Josh
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> > breaks ASLR completely, so Andrew, please drop it for now.
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>
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> Yes, please drop the original.
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Thanks.
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> > I am now looking into how to fix things properly.
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> >
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> > Josh, looking at what you are proposing -- do you see any reason to make
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> > the behavior different in #else branch and in !(current->flags &
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> > PF_RANDOMIZE) case?
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>
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> I was mostly just trying to adapt H.J.'s patch to account for the
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> PF_RANDOMIZE case. Looking at it a bit more, I'm not sure why they
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> would need to be different. H.J., do you recall why you made that
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> change originally?
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How about the patch below instead? It survives my testing, and I believe
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it handles both cases properly.
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Confirmation from the original bug reporter would obviously be a nice
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bonus too :)
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From: Jiri Kosina <jkosina@suse.cz>
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Subject: [PATCH] binfmt_elf: fix PIE execution with randomization disabled
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The case of address space randomization being disabled in runtime through
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randomize_va_space sysctl is not treated properly in load_elf_binary(),
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resulting in SIGKILL coming at exec() time for certain PIE-linked binaries
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in case the randomization has been disabled at runtime prior to calling
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exec().
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Handle the randomize_va_space == 0 case the same way as if we were not
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supporting .text randomization at all.
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Based on original patch by H.J. Lu <hongjiu.lu@intel.com> and
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Josh Boyer <jwboyer@redhat.com>
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Cc: Ingo Molnar <mingo@elte.hu>
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Cc: Jiri Kosina <jkosina@suse.cz>
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Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
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Cc: Russell King <rmk@arm.linux.org.uk>
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Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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---
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fs/binfmt_elf.c | 5 ++++-
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1 files changed, 4 insertions(+), 1 deletions(-)
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diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
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index dd0fdfc..bb11fe4 100644
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--- a/fs/binfmt_elf.c
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+++ b/fs/binfmt_elf.c
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@@ -795,7 +795,10 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
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* might try to exec. This is because the brk will
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* follow the loader, and is not movable. */
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#if defined(CONFIG_X86) || defined(CONFIG_ARM)
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- load_bias = 0;
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+ if (current->flags & PF_RANDOMIZE)
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+ load_bias = 0;
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+ else
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+ load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
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#else
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load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
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#endif
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