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x86/mm: Fix kern_addr_valid() to cope with existing but not present entries
commit34b1999da9
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 - see9a14aefc1d
("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:c40a56a781
("x86/mm/init: Remove freed kernel image areas from alias mapping") for more info. Reported-by: Jiri Olsa <jolsa@redhat.com> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: David Hildenbrand <david@redhat.com> Acked-by: Dave Hansen <dave.hansen@intel.com> Tested-by: Jiri Olsa <jolsa@redhat.com> Cc: <stable@vger.kernel.org> # 4.4+ Link: https://lkml.kernel.org/r/20210819132717.19358-1-rppt@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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1 changed files with 3 additions and 3 deletions
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@ -1355,18 +1355,18 @@ int kern_addr_valid(unsigned long addr)
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return 0;
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p4d = p4d_offset(pgd, addr);
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if (p4d_none(*p4d))
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if (!p4d_present(*p4d))
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return 0;
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pud = pud_offset(p4d, addr);
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if (pud_none(*pud))
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if (!pud_present(*pud))
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return 0;
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if (pud_large(*pud))
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return pfn_valid(pud_pfn(*pud));
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pmd = pmd_offset(pud, addr);
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if (pmd_none(*pmd))
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if (!pmd_present(*pmd))
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return 0;
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if (pmd_large(*pmd))
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