Hi Catalin, 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 :) In the case of arm32 everything is handled via syscall fallback. > 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. > On arm64, while we have a similar access_ok() check, USER_DS is (1 << > VA_BITS) even for compat tasks (52-bit maximum), so it doesn't detect > the end of the user address space for 32-bit tasks. > I agree on this as well, if you remember we discussed it in past. > Is this an issue for other syscalls expecting EFAULT at UINTPTR_MAX and > instead getting a signal? The vdsotest seems to be the only one assuming > this. I don't have a simple solution here since USER_DS currently needs > to be a constant (used in entry.S). > > I could as well argue that this is not a valid ABI test, no real-world > program relying on this behaviour ;). > Ok, but I could argue that unless you manage to prove to me that there is no software out there relying on this behavior, I guess that the safest way to go is to have a check here ;) More than that, being a simple check, it has no performance impact. [...] >>> >>> 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]. > Sorry, just trying to figure out where the compatibility aspect is and > that we don't add some artificial checks only to satisfy a vdsotest case > that may or may not have relevance to any other user program. > No issue Catalin. I understand the implications of the change that I am proposing with this series and I am the first one who wants to get it right. Said that vdsotest follows "pedantically" the ABI spec and I chose it at the beginning of this journey to have as less surprises as I could in the long run. [1] http://man7.org/linux/man-pages/man2/clock_getres.2.html -- Regards, Vincenzo
