Commit 31e67340 authored May 27, 2019 by Rick Edgecombe Committed by Ingo Molnar Jun 03, 2019

mm/vmalloc: Avoid rare case of flushing TLB with weird arguments



In a rare case, flush_tlb_kernel_range() could be called with a start
higher than the end.

In vm_remove_mappings(), in case page_address() returns 0 for all pages
(for example they were all in highmem), _vm_unmap_aliases() will be
called with start = ULONG_MAX, end = 0 and flush = 1.

If at the same time, the vmalloc purge operation is triggered by something
else while the current operation is between remove_vm_area() and
_vm_unmap_aliases(), then the vm mapping just removed will be already
purged. In this case the call of vm_unmap_aliases() may not find any other
mappings to flush and so end up flushing start = ULONG_MAX, end = 0. So
only set flush = true if we find something in the direct mapping that we
need to flush, and this way this can't happen.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Meelis Roos <mroos@linux.ee>
Cc: Nadav Amit <namit@vmware.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 868b104d ("mm/vmalloc: Add flag for freeing of special permsissions")
Link: https://lkml.kernel.org/r/20190527211058.2729-3-rick.p.edgecombe@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8e41f872

mm/vmalloc.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -2125,6 +2125,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
		{
		unsigned long start = ULONG_MAX, end = 0;
		int flush_reset = area->flags & VM_FLUSH_RESET_PERMS;
		int flush_dmap = 0;
		int i;

		/*
		@@ -2163,6 +2164,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
		if (addr) {
		start = min(addr, start);
		end = max(addr + PAGE_SIZE, end);
		flush_dmap = 1;
		}
		}

		@@ -2172,7 +2174,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
		* reset the direct map permissions to the default.
		*/
		set_area_direct_map(area, set_direct_map_invalid_noflush);
		_vm_unmap_aliases(start, end, 1);
		_vm_unmap_aliases(start, end, flush_dmap);
		set_area_direct_map(area, set_direct_map_default_noflush);
		}

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