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Subject[PATCH v4 2/2] vmalloc: Avoid rare case of flushing tlb with weird arguements
Date
In a rare case, flush_tlb_kernel_range() could be called with a start
higher than the end. Most architectures should be fine with with this, but
some may not like it, so avoid doing this.

In vm_remove_mappings(), in case page_address() returns 0 for all pages,
_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.

Fixes: 868b104d7379 ("mm/vmalloc: Add flag for freeing of special permsissions")
Cc: Meelis Roos <mroos@linux.ee>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Nadav Amit <namit@vmware.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
mm/vmalloc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 836888ae01f6..537d1134b40e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2125,6 +2125,7 @@ static void vm_remove_mappings(struct vm_struct *area, int deallocate_pages)
unsigned long addr = (unsigned long)area->addr;
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);
}

--
2.20.1
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