c8d1e4cf83
materializeGCProg allocates a temporary buffer for unrolling a GC program. Unfortunately, when computing the size of the buffer, it rounds *down* the number of bytes needed to store bitmap before rounding up the number of pages needed to store those bytes. The fact that it rounds up to pages usually mitigates the rounding down, but the type from #37470 exists right on the boundary where this doesn't work: type Sequencer struct { htable [1 << 17]uint32 buf []byte } On 64-bit, this GC bitmap is exactly 8 KiB of zeros, followed by three one bits. Hence, this needs 8193 bytes of storage, but the current math in materializeGCProg rounds *down* the three one bits to 8192 bytes. Since this is exactly pageSize, the next step of rounding up to the page size doesn't mitigate this error, and materializeGCProg allocates a buffer that is one byte too small. runGCProg then writes one byte past the end of this buffer, causing either a segfault (if you're lucky!) or memory corruption. Updates #37470. Fixes #37480. Change-Id: Iad24c463c501cd9b1dc1924bc2ad007991a094a0 Reviewed-on: https://go-review.googlesource.com/c/go/+/224417 Run-TryBot: Austin Clements <austin@google.com> Reviewed-by: Cherry Zhang <cherryyz@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> |
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