Messages in this thread | | | Date | Thu, 29 Sep 2011 14:19:29 -0700 | From | Andrew Morton <> | Subject | Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization disabled |
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On Thu, 29 Sep 2011 15:53:59 -0400 Josh Boyer <jwboyer@redhat.com> wrote:
> We've had a bug report[1] of some PIE programs getting a SIGKILL upon exec > if you disable address randomization with: > > echo 0 > /proc/sys/kernel/randomize_va_space > > I tracked this down to get_unmapped_area_prot returning -ENOMEM because > the address being passed in is larger than TASK_SIZE - len for the bss > section of the test executable. That filters back to set_brk returning > an error to load_elf_binary and the SIGKILL being sent around line 872 > of binfmt_elf.c. > > H.J. submitted an upstream bug report [2] as well, but got no feedback > and we can't view it with kernel.org being down anyway. He came up with > the patch below as well, which is what I'm sending on for comments. The > changelog is my addition, so if that is wrong yell at me. > > I wanted to get some more eyes on this, because the current code sets > load_bias to 0 unconditionally on CONFIG_X86 or CONFIG_ARM. I have no > idea why that is. The original execshield patches had an #ifdef on > __i386__ but the patch that was commited to add PIE support has the > CONFIG_X86 setting. >
It appears that Nicolas understood what's going on in there when he wrote e4eab08d6050ad0 ("ARM: 6342/1: fix ASLR of PIE executables"). Alas, that patch's changelog is rather useless.
Help?
Also, please: review and test?
> > [1] https://bugzilla.redhat.com/show_bug.cgi?id=708563 > [2] http://bugzilla.kernel.org/show_bug.cgi?id=36372 > > josh > > --- > > From: H.J. Lu <hongjiu.lu@intel.com> > > Set the load_bias for PIE executables to a non-zero address if no virtual > address is specified. This prevents us from running out of room for all > the various loadable segments when ASLR is disabled. > > Signed-off-by: H.J. Lu <hongjiu.lu@intel.com> > Signed-off-by: Josh Boyer <jwboyer@redhat.com> > > --- > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index 303983f..069ee29 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -794,9 +794,14 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs) > /* Try and get dynamic programs out of the way of the > * default mmap base, as well as whatever program they > * might try to exec. This is because the brk will > - * follow the loader, and is not movable. */ > + * follow the loader, and is not movable. Don't use > + * 0 load address since we may not have room for > + * all loadable segements. */ > #if defined(CONFIG_X86) || defined(CONFIG_ARM) > - load_bias = 0; > + 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
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