Attachment 372622 Details for Bug 199077 – Patch

[patch] Patch

bug-199077-20190621020300.patch (text/plain), 3.04 KB, created by Yusuke Suzuki on 2019-06-21 02:03:01 PDT

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Creator: Yusuke Suzuki

Created: 2019-06-21 02:03:01 PDT

Size: 3.04 KB

patch

obsolete

>Subversion Revision: 246673
>diff --git a/Source/bmalloc/ChangeLog b/Source/bmalloc/ChangeLog
>index ec4db9070e69305067db9d9e52548ab59a43d074..8285b807690afce549b09c8a3b68f979f5d0e913 100644
>--- a/Source/bmalloc/ChangeLog
>+++ b/Source/bmalloc/ChangeLog
>@@ -1,3 +1,28 @@
>+2019-06-21  Yusuke Suzuki  <ysuzuki@apple.com>
>+
>+        [bmalloc] IsoTLS Layout extension initializes one IsoTLSEntry twice
>+        https://bugs.webkit.org/show_bug.cgi?id=199077
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        Found that IsoTLS::ensureEntries can construct the same IsoTLSEntry twice.
>+
>+        1. We have oldLastEntry.
>+        2. In that case, startEntry is oldLastEntry.
>+        3. We found targetEntry with large offset.
>+        4. We reallocate IsoTLS and move entries to the new one. We move [head, oldLastEntry] entries.
>+        5. Finally, if startEntry exists, we newly construct [startEntry, targetEntry]
>+        6. In the above sequence, oldLastEntry (== startEntry) is constructed again.
>+
>+        We can clean up IsoTLS::ensureEntries code, but it is a bit dangerous at this time[1].
>+        So instead, we carefully add defensive code to handle the above case correctly. Later, we will
>+        attempt to clean up IsoTLS::ensureEntries code.
>+
>+        [1]: https://bugs.webkit.org/show_bug.cgi?id=199103
>+
>+        * bmalloc/IsoTLS.cpp:
>+        (bmalloc::IsoTLS::ensureEntries):
>+
> 2019-06-19  Yusuke Suzuki  <ysuzuki@apple.com>
> 
>         [bmalloc] IsoHeap's initialization is racy with IsoHeap::isInitialized
>diff --git a/Source/bmalloc/bmalloc/IsoTLS.cpp b/Source/bmalloc/bmalloc/IsoTLS.cpp
>index c203213b855bdcdc9ed0796fd204ab5d948d8006..f277fda2b6f50cc84eae01d6279143eec9ee5233 100644
>--- a/Source/bmalloc/bmalloc/IsoTLS.cpp
>+++ b/Source/bmalloc/bmalloc/IsoTLS.cpp
>@@ -123,11 +123,24 @@ IsoTLS* IsoTLS::ensureEntries(unsigned offset)
>     }
>     
>     if (startEntry) {
>-        startEntry->walkUpToInclusive(
>-            targetEntry,
>-            [&] (IsoTLSEntry* entry) {
>-                entry->construct(tls->m_data + entry->offset());
>-            });
>+        // FIXME: IsoTLS::ensureEntries can be cleaned up. For example, startEntry should be `oldLastEntry ? oldLastEntry->m_next : layout.head()` instead,
>+        // because we already ensured that `RELEASE_BASSERT(!oldLastEntry || oldLastEntry->offset() < offset)`. And startEntry is never nullptr.
>+        // https://bugs.webkit.org/show_bug.cgi?id=199103
>+        if (oldLastEntry) {
>+            if (oldLastEntry != targetEntry) {
>+                oldLastEntry->m_next->walkUpToInclusive(
>+                    targetEntry,
>+                    [&] (IsoTLSEntry* entry) {
>+                        entry->construct(tls->m_data + entry->offset());
>+                    });
>+            }
>+        } else {
>+            startEntry->walkUpToInclusive(
>+                targetEntry,
>+                [&] (IsoTLSEntry* entry) {
>+                    entry->construct(tls->m_data + entry->offset());
>+                });
>+        }
>         
>         tls->m_lastEntry = targetEntry;
>         tls->m_extent = targetEntry->extent();

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