lkml.org 
[lkml]   [2020]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v4 18/26] arm64: vdso32: Replace TASK_SIZE_32 check in vgettimeofday
    On Tue, Mar 17, 2020 at 04:40:48PM +0000, Vincenzo Frascino wrote:
    > On 3/17/20 3:50 PM, Catalin Marinas wrote:
    > > On Tue, Mar 17, 2020 at 03:04:01PM +0000, Vincenzo Frascino wrote:
    > >> On 3/17/20 2:38 PM, Catalin Marinas wrote:
    > >>> On Tue, Mar 17, 2020 at 12:22:12PM +0000, Vincenzo Frascino wrote:
    > >>
    > >> Can TASK_SIZE > UINTPTR_MAX on an arm64 system?
    > >
    > > TASK_SIZE yes on arm64 but not TASK_SIZE_32. I was asking about the
    > > arm32 check where TASK_SIZE < UINTPTR_MAX. How does the vdsotest return
    > > -EFAULT on arm32? Which code path causes this in the user vdso code?
    >
    > Sorry I got confused because you referred to arch/arm/vdso/vgettimeofday.c which
    > is the arm64 implementation, not the compat one :)

    You figured out (in your subsequent reply) that I was indeed talking
    about arm32 ;).

    > In the case of arm32 everything is handled via syscall fallback.

    So clock_gettime() on arm32 always falls back to the syscall?

    > > My guess is that on arm32 it only fails with -EFAULT in the syscall
    > > fallback path since a copy_to_user() would fail the access_ok() check.
    > > Does it always take the fallback path if ts > TASK_SIZE?
    >
    > Correct, it goes via fallback. The return codes for these syscalls are specified
    > by the ABI [1]. Then I agree with you the way on which arm32 achieves it should
    > be via access_ok() check.

    "it should be" or "it is" on arm32?

    If, on arm32, clock_gettime() is (would be?) handled in the vdso
    entirely, who checks for the pointer outside the accessible address
    space (as per the clock_gettime man page)?

    I'm fine with such check as long as it is consistent across arm32 and
    arm64 compat. Or even on arm64 native between syscall fallback and vdso
    execution. I haven't figured out yet whether this is the case.

    > >>> This last check needs an explanation. If the clock_id is invalid but res
    > >>> is not NULL, we allow it. I don't see where the compatibility issue is,
    > >>> arm32 doesn't have such check.
    > >>
    > >> The case that you are describing has to return -EPERM per ABI spec. This case
    > >> has to return -EINVAL.
    > >>
    > >> The first case is taken care from the generic code. But if we don't do this
    > >> check before on arm64 compat we end up returning the wrong error code.
    > >
    > > I guess I have the same question as above. Where does the arm32 code
    > > return -EINVAL for that case? Did it work correctly before you removed
    > > the TASK_SIZE_32 check?
    >
    > I repeated the test and seems that it was failing even before I removed
    > TASK_SIZE_32. For reasons I can't explain I did not catch it before.
    >
    > The getres syscall should return -EINVAL in the cases specified in [1].

    It states 'clk_id specified is not supported on this system'. Fair
    enough but it doesn't say that it returns -EINVAL only if res == NULL.
    You also don't explain why __cvdso_clock_getres_time32() doesn't already
    detect an invalid clk_id on arm64 compat (but does it on arm32).

    --
    Catalin

    \
     
     \ /
      Last update: 2020-03-17 18:48    [W:3.816 / U:0.248 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site