From d7c532d8894ce806c9af13b8dd3eec975642b348 Mon Sep 17 00:00:00 2001 From: comex Date: Sat, 1 Jul 2023 15:00:39 -0700 Subject: Fixes and workarounds to make UBSan happier on macOS There are still some other issues not addressed here, but it's a start. Workarounds for false-positive reports: - `RasterizerAccelerated`: Put a gigantic array behind a `unique_ptr`, because UBSan has a [hardcoded limit](https://stackoverflow.com/questions/64531383/c-runtime-error-using-fsanitize-undefined-object-has-a-possibly-invalid-vp) of how big it thinks objects can be, specifically when dealing with offset-to-top values used with multiple inheritance. Hopefully this doesn't have a performance impact. - `QueryCacheBase::QueryCacheBase`: Avoid an operation that UBSan thinks is UB even though it at least arguably isn't. See the link in the comment for more information. Fixes for correct reports: - `PageTable`, `Memory`: Use `uintptr_t` values instead of pointers to avoid UB from pointer overflow (when pointer arithmetic wraps around the address space). - `KScheduler::Reload`: `thread->GetOwnerProcess()` can be `nullptr`; avoid calling methods on it in this case. (The existing code returns a garbage reference to a field, which is then passed into `LoadWatchpointArray`, and apparently it's never used, so it's harmless in practice but still triggers UBSan.) - `KAutoObject::Close`: This function calls `this->Destroy()`, which overwrites the beginning of the object with junk (specifically a free list pointer). Then it calls `this->UnregisterWithKernel()`. UBSan complains about a type mismatch because the vtable has been overwritten, and I believe this is indeed UB. `UnregisterWithKernel` also loads `m_kernel` from the 'freed' object, which seems to be technically safe (the overwriting doesn't extend as far as that field), but seems dubious. Switch to a `static` method and load `m_kernel` in advance. --- src/common/page_table.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'src/common') diff --git a/src/common/page_table.h b/src/common/page_table.h index fec8378f3..e653d52ad 100644 --- a/src/common/page_table.h +++ b/src/common/page_table.h @@ -51,7 +51,7 @@ struct PageTable { class PageInfo { public: /// Returns the page pointer - [[nodiscard]] u8* Pointer() const noexcept { + [[nodiscard]] uintptr_t Pointer() const noexcept { return ExtractPointer(raw.load(std::memory_order_relaxed)); } @@ -61,7 +61,7 @@ struct PageTable { } /// Returns the page pointer and attribute pair, extracted from the same atomic read - [[nodiscard]] std::pair PointerType() const noexcept { + [[nodiscard]] std::pair PointerType() const noexcept { const uintptr_t non_atomic_raw = raw.load(std::memory_order_relaxed); return {ExtractPointer(non_atomic_raw), ExtractType(non_atomic_raw)}; } @@ -73,13 +73,13 @@ struct PageTable { } /// Write a page pointer and type pair atomically - void Store(u8* pointer, PageType type) noexcept { - raw.store(reinterpret_cast(pointer) | static_cast(type)); + void Store(uintptr_t pointer, PageType type) noexcept { + raw.store(pointer | static_cast(type)); } /// Unpack a pointer from a page info raw representation - [[nodiscard]] static u8* ExtractPointer(uintptr_t raw) noexcept { - return reinterpret_cast(raw & (~uintptr_t{0} << ATTRIBUTE_BITS)); + [[nodiscard]] static uintptr_t ExtractPointer(uintptr_t raw) noexcept { + return raw & (~uintptr_t{0} << ATTRIBUTE_BITS); } /// Unpack a page type from a page info raw representation -- cgit v1.2.3