Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1335586

Re: [PATCH v2] arm64: add alignment fault hanling

Show all headers | View raw

On Tue, Feb 16, 2016 at 12:21:53PM +0000, Catalin Marinas wrote:
> On Tue, Feb 16, 2016 at 10:57:49AM +0000, Robin Murphy wrote:
> > On 16/02/16 10:31, Will Deacon wrote:
> > >On Tue, Feb 16, 2016 at 04:44:35AM +0000, EunTaik Lee wrote:
> > >>Userspace memory is mapped as below:
> > >>F2A7F000--F2A7FFFF Normal Memory
> > >>F2A80000--F2A80FFF Device nGnRnE
> > >>
> > >>And that userspace application makes a system call
> > >>as below:
> > >>
> > >>-009 |do_strncpy_from_user(inline)
> > >>-009 |strncpy_from_user()
> > >>-010 |getname_flags()
> > >>-011 |user_path_at_empty()
> > >>-012 |user_path_at()
> > >>-013 |SYSC_faccessat(inline)
> > >>-013 |sys_faccessat()
> > >>-014 |__sys_trace(asm)
> > >>  --> |exception
> > >>
> > >>The string spans from 0xF2A7FFC1 to 0xF2A7FFFB.
> > >>
> > >>When do_strncpy_from_user() reads the last (unsigned long)
> > >>value, the alignement fault is triggered. The 8 byte
> > >>from 0xF2A7FFC1 spans to the next page that is mapped as
> > >>Device nGnRnE, which does not allow an unaligned access,
> > >>causes the abort.
> > >>
> > >>The instruction which caused the alignment fault is registered
> > >>in the fixup table but the exception handler does not reach there.
> > >>
> > >>This patch registers a alignment fault handler and fixes up the
> > >>pc if appropriate.
> > >
> > >As discussed with Catalin previously, we should solve this by adding a
> > >guard page rather than handling the fault.
> 
> I don't think we can trivially add this without implementing an arm64
> specific arch_get_unmapped_area().

Even overriding arch_get_unmapped_area doesn't help as much as you might
like since, in the case of something like /dev/mem, the memory is remapped
using remap_pfn_range later on, so you can't necessarily tell what the
final attributes are likely to be when you initially allocate the virtual
space.

Will

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v2] arm64: add alignment fault hanling EunTaik Lee <eun.taik.lee@samsung.com> - 2016-02-16 05:50 +0100
  Re: [PATCH v2] arm64: add alignment fault hanling Will Deacon <will.deacon@arm.com> - 2016-02-16 11:40 +0100
    Re: [PATCH v2] arm64: add alignment fault hanling Robin Murphy <robin.murphy@arm.com> - 2016-02-16 12:00 +0100
      Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-16 13:30 +0100
        Re: [PATCH v2] arm64: add alignment fault hanling Will Deacon <will.deacon@arm.com> - 2016-02-16 17:10 +0100
          Re: [PATCH v2] arm64: add alignment fault hanling Will Deacon <will.deacon@arm.com> - 2016-02-16 18:10 +0100
            Re: [PATCH v2] arm64: add alignment fault hanling Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-16 20:00 +0100
              Re: [PATCH v2] arm64: add alignment fault hanling Arjan van de Ven <arjan@linux.intel.com> - 2016-02-16 22:40 +0100
                Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-17 00:10 +0100
                Re: [PATCH v2] arm64: add alignment fault hanling Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-17 01:30 +0100
              Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-19 19:20 +0100
                Re: [PATCH v2] arm64: add alignment fault hanling Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-19 23:10 +0100
          Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-16 18:20 +0100
  Re: [PATCH v2] arm64: add alignment fault hanling Catalin Marinas <catalin.marinas@arm.com> - 2016-02-16 18:20 +0100

csiph-web