From: Mike Rapoport Date: Thu, 19 Aug 2021 13:27:17 +0000 (+0300) Subject: x86/mm: Fix kern_addr_valid() to cope with existing but not present entries X-Git-Tag: v5.10.79~812 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=12551b75b00b8d1de3a944ab44c997bee7c9bce0;p=platform%2Fkernel%2Flinux-rpi.git x86/mm: Fix kern_addr_valid() to cope with existing but not present entries commit 34b1999da935a33be6239226bfa6cd4f704c5c88 upstream. Jiri Olsa reported a fault when running: # cat /proc/kallsyms | grep ksys_read ffffffff8136d580 T ksys_read # objdump -d --start-address=0xffffffff8136d580 --stop-address=0xffffffff8136d590 /proc/kcore /proc/kcore: file format elf64-x86-64 Segmentation fault general protection fault, probably for non-canonical address 0xf887ffcbff000: 0000 [#1] SMP PTI CPU: 12 PID: 1079 Comm: objdump Not tainted 5.14.0-rc5qemu+ #508 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-4.fc34 04/01/2014 RIP: 0010:kern_addr_valid Call Trace: read_kcore ? rcu_read_lock_sched_held ? rcu_read_lock_sched_held ? rcu_read_lock_sched_held ? trace_hardirqs_on ? rcu_read_lock_sched_held ? lock_acquire ? lock_acquire ? rcu_read_lock_sched_held ? lock_acquire ? rcu_read_lock_sched_held ? rcu_read_lock_sched_held ? rcu_read_lock_sched_held ? lock_release ? _raw_spin_unlock ? __handle_mm_fault ? rcu_read_lock_sched_held ? lock_acquire ? rcu_read_lock_sched_held ? lock_release proc_reg_read ? vfs_read vfs_read ksys_read do_syscall_64 entry_SYSCALL_64_after_hwframe The fault happens because kern_addr_valid() dereferences existent but not present PMD in the high kernel mappings. Such PMDs are created when free_kernel_image_pages() frees regions larger than 2Mb. In this case, a part of the freed memory is mapped with PMDs and the set_memory_np_noalias() -> ... -> __change_page_attr() sequence will mark the PMD as not present rather than wipe it completely. Have kern_addr_valid() check whether higher level page table entries are present before trying to dereference them to fix this issue and to avoid similar issues in the future. Stable backporting note: ------------------------ Note that the stable marking is for all active stable branches because there could be cases where pagetable entries exist but are not valid - see 9a14aefc1d28 ("x86: cpa, fix lookup_address"), for example. So make sure to be on the safe side here and use pXY_present() accessors rather than pXY_none() which could #GP when accessing pages in the direct map. Also see: c40a56a7818c ("x86/mm/init: Remove freed kernel image areas from alias mapping") for more info. Reported-by: Jiri Olsa Signed-off-by: Mike Rapoport Signed-off-by: Borislav Petkov Reviewed-by: David Hildenbrand Acked-by: Dave Hansen Tested-by: Jiri Olsa Cc: # 4.4+ Link: https://lkml.kernel.org/r/20210819132717.19358-1-rppt@kernel.org Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index b5a3fa4..067ca92 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -1389,18 +1389,18 @@ int kern_addr_valid(unsigned long addr) return 0; p4d = p4d_offset(pgd, addr); - if (p4d_none(*p4d)) + if (!p4d_present(*p4d)) return 0; pud = pud_offset(p4d, addr); - if (pud_none(*pud)) + if (!pud_present(*pud)) return 0; if (pud_large(*pud)) return pfn_valid(pud_pfn(*pud)); pmd = pmd_offset(pud, addr); - if (pmd_none(*pmd)) + if (!pmd_present(*pmd)) return 0; if (pmd_large(*pmd))