Hi Kirill,
On Mon, Jul 13, 2015 at 1:54 PM, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> MPX setups private anonymous mapping, but uses vma->vm_ops too.
> This can confuse core VM, as it relies on vm->vm_ops to distinguish
> file VMAs from anonymous.
>
> As result we will get SIGBUS, because handle_pte_fault() thinks it's
> file VMA without vm_ops->fault and it doesn't know how to handle the
> situation properly.
>
> Let's fix that by not setting ->vm_ops.
>
> We don't really need ->vm_ops here: MPX VMA can be detected with VM_MPX
> flag. And vma_merge() will not merge MPX VMA with non-MPX VMA, because
> ->vm_flags won't match.
>
> The only thing left is name of VMA. I'm not sure if it's part of ABI, or
> we can just drop it. The patch keep it by providing arch_vma_name() on x86.
>
> Build tested only.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> arch/x86/mm/mmap.c | 7 +++++++
> arch/x86/mm/mpx.c | 20 +-------------------
> 2 files changed, 8 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 9d518d693b4b..844b06d67df4 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -126,3 +126,10 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
> mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> }
> }
> +
> +const char *arch_vma_name(struct vm_area_struct *vma)
> +{
> + if (vma->vm_flags & VM_MPX)
> + return "[mpx]";
> + return NULL;
> +}
I sure that I'm missing something important. This function stores
"[mpx]" string on this function stack and returns the pointer to that
address. In current flow, this address is visible and accessible,
however in can be a different in general case.
> diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
> index c439ec478216..4d1c11c07fe1 100644
> --- a/arch/x86/mm/mpx.c
> +++ b/arch/x86/mm/mpx.c
> @@ -18,26 +18,9 @@
> #include <asm/processor.h>
> #include <asm/fpu-internal.h>
>
> -static const char *mpx_mapping_name(struct vm_area_struct *vma)
> -{
> - return "[mpx]";
> -}
> -
> -static struct vm_operations_struct mpx_vma_ops = {
> - .name = mpx_mapping_name,
> -};
> -
> -static int is_mpx_vma(struct vm_area_struct *vma)
> -{
> - return (vma->vm_ops == &mpx_vma_ops);
> -}
> -
> /*
> * This is really a simplified "vm_mmap". it only handles MPX
> * bounds tables (the bounds directory is user-allocated).
> - *
> - * Later on, we use the vma->vm_ops to uniquely identify these
> - * VMAs.
> */
> static unsigned long mpx_mmap(unsigned long len)
> {
> @@ -83,7 +66,6 @@ static unsigned long mpx_mmap(unsigned long len)
> ret = -ENOMEM;
> goto out;
> }
> - vma->vm_ops = &mpx_vma_ops;
>
> if (vm_flags & VM_LOCKED) {
> up_write(&mm->mmap_sem);
> @@ -661,7 +643,7 @@ static int zap_bt_entries(struct mm_struct *mm,
> * so stop immediately and return an error. This
> * probably results in a SIGSEGV.
> */
> - if (!is_mpx_vma(vma))
> + if (!(vma->vm_flags & VM_MPX))
> return -EINVAL;
>
> len = min(vma->vm_end, end) - addr;
> --
> 2.1.4
>
> --
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--
Leon Romanovsky | Independent Linux Consultant
www.leon.nu | leon@xxxxxxx
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