Re: [PATCH 3.18 04/57] vm: add VM_FAULT_SIGSEGV handling support

From: Luis Henriques
Date: Mon Feb 16 2015 - 04:49:33 EST

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On Tue, Feb 10, 2015 at 12:22:41PM +0400, Konstantin Khlebnikov wrote:
> I've found regression:
>
> [ 257.139907] ================================================
> [ 257.139909] [ BUG: lock held when returning to user space! ]
> [ 257.139912] 3.18.6-debug+ #161 Tainted: G U
> [ 257.139914] ------------------------------------------------
> [ 257.139916] python/22843 is leaving the kernel with locks still held!
> [ 257.139918] 1 lock held by python/22843:
> [ 257.139920] #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8104e4c2>]
> __do_page_fault+0x162/0x570
>
> upstream commit 7fb08eca45270d0ae86e1ad9d39c40b7a55d0190 must be backported too.
>

I guess the same regression can be found in the 3.16 kernel as it also
includes a backport of 33692f27597f ("vm: add VM_FAULT_SIGSEGV
handling support"). I'll queue 7fb08eca4527 ("x86: mm: move mmap_sem
unlock from mm_fault_error() to caller") as well.

Cheers,
--
Luís

> On Wed, Feb 4, 2015 at 2:13 AM, Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > 3.18-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> >
> > commit 33692f27597fcab536d7cbbcc8f52905133e4aa7 upstream.
> >
> > The core VM already knows about VM_FAULT_SIGBUS, but cannot return a
> > "you should SIGSEGV" error, because the SIGSEGV case was generally
> > handled by the caller - usually the architecture fault handler.
> >
> > That results in lots of duplication - all the architecture fault
> > handlers end up doing very similar "look up vma, check permissions, do
> > retries etc" - but it generally works. However, there are cases where
> > the VM actually wants to SIGSEGV, and applications _expect_ SIGSEGV.
> >
> > In particular, when accessing the stack guard page, libsigsegv expects a
> > SIGSEGV. And it usually got one, because the stack growth is handled by
> > that duplicated architecture fault handler.
> >
> > However, when the generic VM layer started propagating the error return
> > from the stack expansion in commit fee7e49d4514 ("mm: propagate error
> > from stack expansion even for guard page"), that now exposed the
> > existing VM_FAULT_SIGBUS result to user space. And user space really
> > expected SIGSEGV, not SIGBUS.
> >
> > To fix that case, we need to add a VM_FAULT_SIGSEGV, and teach all those
> > duplicate architecture fault handlers about it. They all already have
> > the code to handle SIGSEGV, so it's about just tying that new return
> > value to the existing code, but it's all a bit annoying.
> >
> > This is the mindless minimal patch to do this. A more extensive patch
> > would be to try to gather up the mostly shared fault handling logic into
> > one generic helper routine, and long-term we really should do that
> > cleanup.
> >
> > Just from this patch, you can generally see that most architectures just
> > copied (directly or indirectly) the old x86 way of doing things, but in
> > the meantime that original x86 model has been improved to hold the VM
> > semaphore for shorter times etc and to handle VM_FAULT_RETRY and other
> > "newer" things, so it would be a good idea to bring all those
> > improvements to the generic case and teach other architectures about
> > them too.
> >
> > Reported-and-tested-by: Takashi Iwai <tiwai@xxxxxxx>
> > Tested-by: Jan Engelhardt <jengelh@xxxxxxx>
> > Acked-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx> # "s390 still compiles and boots"
> > Cc: linux-arch@xxxxxxxxxxxxxxx
> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >
> > ---
> > arch/alpha/mm/fault.c | 2 ++
> > arch/arc/mm/fault.c | 2 ++
> > arch/avr32/mm/fault.c | 2 ++
> > arch/cris/mm/fault.c | 2 ++
> > arch/frv/mm/fault.c | 2 ++
> > arch/ia64/mm/fault.c | 2 ++
> > arch/m32r/mm/fault.c | 2 ++
> > arch/m68k/mm/fault.c | 2 ++
> > arch/metag/mm/fault.c | 2 ++
> > arch/microblaze/mm/fault.c | 2 ++
> > arch/mips/mm/fault.c | 2 ++
> > arch/mn10300/mm/fault.c | 2 ++
> > arch/openrisc/mm/fault.c | 2 ++
> > arch/parisc/mm/fault.c | 2 ++
> > arch/powerpc/mm/copro_fault.c | 2 +-
> > arch/powerpc/mm/fault.c | 2 ++
> > arch/s390/mm/fault.c | 6 ++++++
> > arch/score/mm/fault.c | 2 ++
> > arch/sh/mm/fault.c | 2 ++
> > arch/sparc/mm/fault_32.c | 2 ++
> > arch/sparc/mm/fault_64.c | 2 ++
> > arch/tile/mm/fault.c | 2 ++
> > arch/um/kernel/trap.c | 2 ++
> > arch/x86/mm/fault.c | 2 ++
> > arch/xtensa/mm/fault.c | 2 ++
> > drivers/staging/lustre/lustre/llite/vvp_io.c | 2 +-
> > include/linux/mm.h | 6 ++++--
> > mm/gup.c | 4 ++--
> > mm/ksm.c | 2 +-
> > 29 files changed, 61 insertions(+), 7 deletions(-)
> >
> > --- a/arch/alpha/mm/fault.c
> > +++ b/arch/alpha/mm/fault.c
> > @@ -156,6 +156,8 @@ retry:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/arc/mm/fault.c
> > +++ b/arch/arc/mm/fault.c
> > @@ -161,6 +161,8 @@ good_area:
> >
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> >
> > --- a/arch/avr32/mm/fault.c
> > +++ b/arch/avr32/mm/fault.c
> > @@ -142,6 +142,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/cris/mm/fault.c
> > +++ b/arch/cris/mm/fault.c
> > @@ -176,6 +176,8 @@ retry:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/frv/mm/fault.c
> > +++ b/arch/frv/mm/fault.c
> > @@ -168,6 +168,8 @@ asmlinkage void do_page_fault(int datamm
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/ia64/mm/fault.c
> > +++ b/arch/ia64/mm/fault.c
> > @@ -172,6 +172,8 @@ retry:
> > */
> > if (fault & VM_FAULT_OOM) {
> > goto out_of_memory;
> > + } else if (fault & VM_FAULT_SIGSEGV) {
> > + goto bad_area;
> > } else if (fault & VM_FAULT_SIGBUS) {
> > signal = SIGBUS;
> > goto bad_area;
> > --- a/arch/m32r/mm/fault.c
> > +++ b/arch/m32r/mm/fault.c
> > @@ -200,6 +200,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/m68k/mm/fault.c
> > +++ b/arch/m68k/mm/fault.c
> > @@ -145,6 +145,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto map_err;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto bus_err;
> > BUG();
> > --- a/arch/metag/mm/fault.c
> > +++ b/arch/metag/mm/fault.c
> > @@ -141,6 +141,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/microblaze/mm/fault.c
> > +++ b/arch/microblaze/mm/fault.c
> > @@ -224,6 +224,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/mips/mm/fault.c
> > +++ b/arch/mips/mm/fault.c
> > @@ -158,6 +158,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/mn10300/mm/fault.c
> > +++ b/arch/mn10300/mm/fault.c
> > @@ -262,6 +262,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/openrisc/mm/fault.c
> > +++ b/arch/openrisc/mm/fault.c
> > @@ -171,6 +171,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/parisc/mm/fault.c
> > +++ b/arch/parisc/mm/fault.c
> > @@ -256,6 +256,8 @@ good_area:
> > */
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto bad_area;
> > BUG();
> > --- a/arch/powerpc/mm/copro_fault.c
> > +++ b/arch/powerpc/mm/copro_fault.c
> > @@ -76,7 +76,7 @@ int copro_handle_mm_fault(struct mm_stru
> > if (*flt & VM_FAULT_OOM) {
> > ret = -ENOMEM;
> > goto out_unlock;
> > - } else if (*flt & VM_FAULT_SIGBUS) {
> > + } else if (*flt & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV)) {
> > ret = -EFAULT;
> > goto out_unlock;
> > }
> > --- a/arch/powerpc/mm/fault.c
> > +++ b/arch/powerpc/mm/fault.c
> > @@ -444,6 +444,8 @@ good_area:
> > */
> > fault = handle_mm_fault(mm, vma, address, flags);
> > if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
> > + if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > rc = mm_fault_error(regs, address, fault);
> > if (rc >= MM_FAULT_RETURN)
> > goto bail;
> > --- a/arch/s390/mm/fault.c
> > +++ b/arch/s390/mm/fault.c
> > @@ -374,6 +374,12 @@ static noinline void do_fault_error(stru
> > do_no_context(regs);
> > else
> > pagefault_out_of_memory();
> > + } else if (fault & VM_FAULT_SIGSEGV) {
> > + /* Kernel mode? Handle exceptions or die */
> > + if (!user_mode(regs))
> > + do_no_context(regs);
> > + else
> > + do_sigsegv(regs, SEGV_MAPERR);
> > } else if (fault & VM_FAULT_SIGBUS) {
> > /* Kernel mode? Handle exceptions or die */
> > if (!user_mode(regs))
> > --- a/arch/score/mm/fault.c
> > +++ b/arch/score/mm/fault.c
> > @@ -114,6 +114,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/sh/mm/fault.c
> > +++ b/arch/sh/mm/fault.c
> > @@ -353,6 +353,8 @@ mm_fault_error(struct pt_regs *regs, uns
> > } else {
> > if (fault & VM_FAULT_SIGBUS)
> > do_sigbus(regs, error_code, address);
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + bad_area(regs, error_code, address);
> > else
> > BUG();
> > }
> > --- a/arch/sparc/mm/fault_32.c
> > +++ b/arch/sparc/mm/fault_32.c
> > @@ -249,6 +249,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/sparc/mm/fault_64.c
> > +++ b/arch/sparc/mm/fault_64.c
> > @@ -446,6 +446,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/tile/mm/fault.c
> > +++ b/arch/tile/mm/fault.c
> > @@ -444,6 +444,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/arch/um/kernel/trap.c
> > +++ b/arch/um/kernel/trap.c
> > @@ -80,6 +80,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM) {
> > goto out_of_memory;
> > + } else if (fault & VM_FAULT_SIGSEGV) {
> > + goto out;
> > } else if (fault & VM_FAULT_SIGBUS) {
> > err = -EACCES;
> > goto out;
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -905,6 +905,8 @@ mm_fault_error(struct pt_regs *regs, uns
> > if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
> > VM_FAULT_HWPOISON_LARGE))
> > do_sigbus(regs, error_code, address, fault);
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + bad_area_nosemaphore(regs, error_code, address);
> > else
> > BUG();
> > }
> > --- a/arch/xtensa/mm/fault.c
> > +++ b/arch/xtensa/mm/fault.c
> > @@ -117,6 +117,8 @@ good_area:
> > if (unlikely(fault & VM_FAULT_ERROR)) {
> > if (fault & VM_FAULT_OOM)
> > goto out_of_memory;
> > + else if (fault & VM_FAULT_SIGSEGV)
> > + goto bad_area;
> > else if (fault & VM_FAULT_SIGBUS)
> > goto do_sigbus;
> > BUG();
> > --- a/drivers/staging/lustre/lustre/llite/vvp_io.c
> > +++ b/drivers/staging/lustre/lustre/llite/vvp_io.c
> > @@ -632,7 +632,7 @@ static int vvp_io_kernel_fault(struct vv
> > return 0;
> > }
> >
> > - if (cfio->fault.ft_flags & VM_FAULT_SIGBUS) {
> > + if (cfio->fault.ft_flags & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV)) {
> > CDEBUG(D_PAGE, "got addr %p - SIGBUS\n", vmf->virtual_address);
> > return -EFAULT;
> > }
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1054,6 +1054,7 @@ static inline int page_mapped(struct pag
> > #define VM_FAULT_WRITE 0x0008 /* Special case for get_user_pages */
> > #define VM_FAULT_HWPOISON 0x0010 /* Hit poisoned small page */
> > #define VM_FAULT_HWPOISON_LARGE 0x0020 /* Hit poisoned large page. Index encoded in upper bits */
> > +#define VM_FAULT_SIGSEGV 0x0040
> >
> > #define VM_FAULT_NOPAGE 0x0100 /* ->fault installed the pte, not return page */
> > #define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned page */
> > @@ -1062,8 +1063,9 @@ static inline int page_mapped(struct pag
> >
> > #define VM_FAULT_HWPOISON_LARGE_MASK 0xf000 /* encodes hpage index for large hwpoison */
> >
> > -#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_HWPOISON | \
> > - VM_FAULT_FALLBACK | VM_FAULT_HWPOISON_LARGE)
> > +#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
> > + VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
> > + VM_FAULT_FALLBACK)
> >
> > /* Encode hstate index for a hwpoisoned large page */
> > #define VM_FAULT_SET_HINDEX(x) ((x) << 12)
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -296,7 +296,7 @@ static int faultin_page(struct task_stru
> > return -ENOMEM;
> > if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
> > return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
> > - if (ret & VM_FAULT_SIGBUS)
> > + if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
> > return -EFAULT;
> > BUG();
> > }
> > @@ -571,7 +571,7 @@ int fixup_user_fault(struct task_struct
> > return -ENOMEM;
> > if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
> > return -EHWPOISON;
> > - if (ret & VM_FAULT_SIGBUS)
> > + if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
> > return -EFAULT;
> > BUG();
> > }
> > --- a/mm/ksm.c
> > +++ b/mm/ksm.c
> > @@ -376,7 +376,7 @@ static int break_ksm(struct vm_area_stru
> > else
> > ret = VM_FAULT_WRITE;
> > put_page(page);
> > - } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
> > + } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
> > /*
> > * We must loop because handle_mm_fault() may back out if there's
> > * any difficulty e.g. if pte accessed bit gets updated concurrently.
> >
> >
> > --
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