• Daniel Lehmann's avatar
    [wasm] Add missing scopes for code modification · eb57c722
    Daniel Lehmann authored
    This is the second CL in a line of two (see crrev.com/c/2835237) to
    bring write-protection to the WebAssembly code space. The previous CL
    changed the page permissions from W^X (only either writable or
    executable can be active, but never both) to write-protection (due to
    concurrent execution in the main thread). However, write-protection
    still did not work, because in several places the code space is
    modified without properly switching it to writable beforehand.
    
    This CL fixes --wasm-write-protect-code-memory such that it can now be
    enabled again (with potentially high overhead due to frequent page
    protection switches). For that, it adds the missing switching to
    writable by adding {NativeModuleModificationScope} objects (similar to
    the already existing {CodeSpaceWriteScope} objects for Apple M1
    hardware).
    
    This CL also fixes a race condition between checking for the current
    writable permission and actually setting the permission, by protecting
    the counter of currently active writers with the same lock as the
    {WasmCodeAllocator} itself. (Before multi-threaded compilation, this
    was not necessary.)
    
    Finally, this CL also changes the {Mutex} protecting the
    {WasmCodeAllocator} to a {RecursiveMutex} because it can be requested
    multiple times in the call hierarchy of the same thread, which would
    cause a deadlock otherwise. Since {TryLock()} of a {RecursiveMutex}
    never fails, this also removes the (now failing) DCHECKs.
    
    R=clemensb@chromium.org
    CC=​​jkummerow@chromium.org
    
    Bug: v8:11663
    Change-Id: I4db27ad0a9348021b0b663dbe88b3432a4d8d6b5
    Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng
    Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2835238
    Commit-Queue: Daniel Lehmann <dlehmann@google.com>
    Reviewed-by: 's avatarClemens Backes <clemensb@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#74163}
    eb57c722
wasm-code-manager.h 39.7 KB