fix: insert critical overflow checks preventing heap corruption #3077
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This was referenced Jan 28, 2022
ggreif
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No idea. Not urgent.
…On 1/28/22, Claudio Russo ***@***.***> wrote:
@crusso commented on this pull request.
> get_data_size ^^
+ compile_const_64 0x1_0000_0000L ^^
Sure, I've done that elsewhere, but is it actually cheaper? I still need to
convert the i64 to a i32 for the conditional I think.
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…sts (#3085) #3077 added an expensive, but necessary overflow check to `alloc_words`, to prevent allocating addresses outside the 32-bit heap. * This PR optimizes that check to avoid the conditional test by doing the page diff arithmetic in u64s, relying on `grow_memory` to trap when asked to grow beyond 2^16 pages. * fixes test `run-drun/oom-update` to actually use an update (not query) method as advertised. I wonder why `grow_memory` is marked `inline_never`? Seems like we'd save a function call on each allocation...
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Fixes two classes of
u32-undetected overflow bugs that could corrupt heap, stable variables, or both:alloc_wordswasn't checking validity of addresses, leading to possible (and observed) heap corruption.buffer_sizewasn't checking overflow of 32-bit size pre-computation.The first is fixed using an overflow detecting add function of Rust.
The second is checked by using a local
i64in each type-directed size function. These functions are MV and return twoi32s (for the data buffer and (vestigial) reference buffer sizes. I did not modify the functions to return 2i64s because our MultiValue emulation only supporti32at the moment.Fixes #3068.