linux-kernel - [tip:x86/urgent] mm/vmalloc: Avoid rare case of flushing TLB with weird arguments

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Date:   Mon, 3 Jun 2019 05:59:46 -0700
From:   tip-bot for Rick Edgecombe <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, mroos@...ux.ee,
        dave.hansen@...el.com, luto@...nel.org, bp@...en8.de,
        rick.p.edgecombe@...el.com, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, hpa@...or.com, davem@...emloft.net,
        peterz@...radead.org, namit@...are.com, tglx@...utronix.de
Subject: [tip:x86/urgent] mm/vmalloc: Avoid rare case of flushing TLB with
 weird arguments

Commit-ID:  31e67340cc65edfd9dac5ef26f81de8414ce5906
Gitweb:     https://git.kernel.org/tip/31e67340cc65edfd9dac5ef26f81de8414ce5906
Author:     Rick Edgecombe <rick.p.edgecombe@...el.com>
AuthorDate: Mon, 27 May 2019 14:10:58 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 3 Jun 2019 11:47:25 +0200

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@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: David S. Miller <davem@...emloft.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Meelis Roos <mroos@...ux.ee>
Cc: Nadav Amit <namit@...are.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Fixes: 868b104d7379 ("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@...nel.org>
---
 mm/vmalloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 93b2dca2aadb..4c9e150e5ad3 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 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);
 }