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Date:   Thu, 22 Oct 2020 20:27:22 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Nick Desaulniers <ndesaulniers@google.com>
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Subject: Re: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move
 rw_copy_check_uvector() into lib/iov_iter.c"
Message-ID: <20201022192722.GW3576660@ZenIV.linux.org.uk>
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On Thu, Oct 22, 2020 at 08:24:58PM +0100, Al Viro wrote:
> On Thu, Oct 22, 2020 at 12:04:52PM -0700, Nick Desaulniers wrote:
> 
> > Passing an `unsigned long` as an `unsigned int` does no such
> > narrowing: https://godbolt.org/z/TvfMxe (same vice-versa, just tail
> > calls, no masking instructions).
> > So if rw_copy_check_uvector() is inlined into import_iovec() (looking
> > at the mainline@1028ae406999), then children calls of
> > `rw_copy_check_uvector()` will be interpreting the `nr_segs` register
> > unmodified, ie. garbage in the upper 32b.
> 
> FWIW,
> 
> void f(unsinged long v)

s/unsinged/unsigned/, obviously...