On Mon, 2007-07-09 at 16:48, Scott Wood wrote:
> In older versions of glibc (through 2.3), the dynamic linker executes a
> small amount of code from the data segment, which is not marked as
> executable. A recent change (commit 9ba4ace39fdfe22268daca9f28c5df384ae462cf)
> stops this from working; there should be a deprecation period before
> older glibc versions stop working.
>
> The problem has been observed on glibc 2.2. While glibc 2.3 has the same
> code, I did not see the problem; it may be that it accesses the page in
> question as data before executing from it, and thus it is already mapped.
>
> Note that this only applies to the classic 32-bit PowerPC MMU and the
> MPC8xx MMU, not Book E, 64-bit, etc. These MMUs do not support per-page
> no-exec, and thus this patch isn't taking away any effective protection
> enforcement. Currently, such accesses will fail only if the page in
> question has not already been faulted on (and thus mapped).
>
> Signed-off-by: Scott Wood <[EMAIL PROTECTED]>
> ---
Well now. I've spent a good chunk of today with Our Friend, git-bisect,
verifying that, in fact, the commit 9ba4ace39fdfe22268daca9f28c5df384ae462cf
breaks the 8641 HPCN port. init doesn't run off an old NFS'ed root FS
worth a Steven J Hill of beans.
But luckily, this gave me the opportunity to then realize that
we should give a great big...
Amen-brother-by: Jon Loeliger <[EMAIL PROTECTED]>
to this patch from Scott.
So, an official plea to Paul to apply this to his tree.
jdl
> v2: Added to the changelog to explain why this change isn't harmful.
>
> arch/powerpc/mm/fault.c | 22 +++++++++++++++++++++-
> 1 files changed, 21 insertions(+), 1 deletions(-)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 0ece513..2445512 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -125,6 +125,18 @@ static void do_dabr(struct pt_regs *regs, unsigned long
> address,
> }
> #endif /* !(CONFIG_4xx || CONFIG_BOOKE)*/
>
> +#ifdef CONFIG_PPC32
> +static void warn_exec_from_noexec(void)
> +{
> + if (printk_ratelimit())
> + printk(KERN_WARNING "Process %s (%d) attempted to execute from "
> + "a non-executable page.\n"
> + KERN_WARNING "This may stop working in future kernels. "
> + "Please upgrade your libc.\n",
> + current->comm, current->pid);
> +}
> +#endif
> +
> /*
> * For 600- and 800-family processors, the error_code parameter is DSISR
> * for a data fault, SRR1 for an instruction fault. For 400-family processors
> @@ -283,8 +295,16 @@ good_area:
> /* protection fault */
> if (error_code & DSISR_PROTFAULT)
> goto bad_area;
> - if (!(vma->vm_flags & VM_EXEC))
> + if (!(vma->vm_flags & VM_EXEC)) {
> +#ifdef CONFIG_PPC32
> + if (vma->vm_flags & VM_READ)
> + warn_exec_from_noexec();
> + else
> + goto bad_area;
> +#else
> goto bad_area;
> +#endif
> + }
> #else
> pte_t *ptep;
> pmd_t *pmdp;
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