* Will Deacon <will@xxxxxxxxxx> [210422 09:01]: > On Tue, Apr 20, 2021 at 04:50:12PM +0000, Liam Howlett wrote: > > arm64_notify_segfault() was written to decide on the si_code from the > > assembly emulation of the swp_handler(), but was also used for the > > signal generation from failed access_ok() and unaligned instructions. > > > > When access_ok() fails, there is no need to search for the offending > > address in the VMA space. Instead, simply set the error to SIGSEGV with > > si_code SEGV_ACCERR. > > > > Change the return code from emulate_swpX() when there is an unaligned > > pointer so the caller can differentiate from the EFAULT. It is > > unnecessary to search the VMAs in the case of an unaligned pointer. > > This change uses SIGSEGV and SEGV_ACCERR instead of SIGBUS to keep with > > what was returned before. > > > > Fixes: bd35a4adc413 (arm64: Port SWP/SWPB emulation support from arm) > > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > > --- > > arch/arm64/kernel/armv8_deprecated.c | 20 +++++++++++++------- > > Can you give an example of something that is fixed by this, please? At first > glance, it doesn't look like it changes the user-visible behaviour. In short, when !access_ok(), don't return SEGV_MAPERR. access_ok() is defined as __range_ok() which checks if the address is a userspace address. If the access is not okay, then the return should be SEGV_ACCERR. However, if the address is above any known VMA, then the return will be SEGV_MAPERR. Isn't this a bug? Right now this particular bug is masked almost always by the fact that find_vma() will return SIGV_ACCERR unless it's abvove any known VMA, but patch 3 in this series will alter the behaviour and thus, I wanted to fix the bug here before fixing that bug. > > We should also be compatible with arch/arm/ here (see set_segfault()). Yes, the same error exists there it seems. If my solution is acceptable, I can expand it to include the same change there. Thanks, Liam
