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
