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fix AsByteSliceMut using raw pointers with bad provenance #780

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merged 2 commits into from
Apr 20, 2019

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RalfJung
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@RalfJung RalfJung commented Apr 19, 2019

&mut slice[0] as *mut _ is a raw pointer that can only be used for the first element.

slice.as_mut_ptr() is not only shorter, but also correctly returns a pointer that can be used for the entire slice.

(Found by running the test suite in Miri.)

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dhardy commented Apr 19, 2019

LGTM but I think you have a few more tweaks to add before merging.

@RalfJung
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Do you want me to add RalfJung@8303309?

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Indeed that commit is the only other change I need to make all test suites pass (except for fill_bytes which I don't know how to fix). So I added it here.

I also have some patches to make running Miri on the test suite feasible; I will submit those separately.

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dhardy commented Apr 20, 2019

These look good to me thanks! Yes, fill_bytes and test runners can have separate PRs.

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Okay, so this is ready to get merged then?

@dhardy dhardy merged commit 476cb6d into rust-random:master Apr 20, 2019
@@ -183,7 +183,8 @@ where <R as BlockRngCore>::Results: AsRef<[u32]> + AsMut<[u32]>
let read_u64 = |results: &[u32], index| {
if cfg!(any(target_arch = "x86", target_arch = "x86_64")) {
// requires little-endian CPU supporting unaligned reads:
unsafe { *(&results[index] as *const u32 as *const u64) }
let ptr: *const u64 = results[index..index+1].as_ptr() as *const u64;
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This range still only covers 1 element, not 2 elements, as it uses .. instead of ..=.

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Yeah, I fixed that in #784

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Didn't notice that commit :)

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3 participants