On Mon, Feb 13, 2023 at 7:39 PM Heiko Carstens <hca@xxxxxxxxxxxxx> wrote: > > Baoquan He reported lots of KFENCE reports when /proc/kcore is read, > e.g. with crash or even simpler with dd: > > BUG: KFENCE: invalid read in copy_from_kernel_nofault+0x5e/0x120 > Invalid read at 0x00000000f4f5149f: > copy_from_kernel_nofault+0x5e/0x120 > read_kcore+0x6b2/0x870 > proc_reg_read+0x9a/0xf0 > vfs_read+0x94/0x270 > ksys_read+0x70/0x100 > __do_syscall+0x1d0/0x200 > system_call+0x82/0xb0 > > The reason for this is that read_kcore() simply reads memory that might > have been unmapped by KFENCE with copy_from_kernel_nofault(). Any fault due > to pages being unmapped by KFENCE would be handled gracefully by the fault > handler (exception table fixup). > > However the s390 fault handler first reports the fault, and only afterwards > would perform the exception table fixup. Most architectures have this in > reversed order, which also avoids the false positive KFENCE reports when an > unmapped page is accessed. > > Therefore change the s390 fault handler so it handles exception table > fixups before KFENCE page faults are reported. > > Reported-by: Baoquan He <bhe@xxxxxxxxxx> > Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx> Acked-by: Alexander Potapenko <glider@xxxxxxxxxx>
