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<p style="color: #777777;">
<a href="https://gitlab.com/smuellerDD">Stephan Mueller</a>
commented on a
discussion on <a href="https://gitlab.com/gnutls/gnutls/-/merge_requests/1404#note_551236000">lib/accelerated/afalg.c</a>:
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<pre style="margin: 0;">-<span id="LC388" class="line" lang="c"> <span class="n" style="color: #333;">iov</span><span class="p">[</span><span class="mi" style="color: #099;"><span class="idiff left right deletion">1</span></span><span class="p">].</span><span class="n" style="color: #333;">iov_base</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">plain</span><span class="p">;</span></span>
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389
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<pre style="margin: 0;">-<span id="LC389" class="line" lang="c"> <span class="n" style="color: #333;">iov</span><span class="p">[</span><span class="mi" style="color: #099;"><span class="idiff left right deletion">1</span></span><span class="p">].</span><span class="n" style="color: #333;">iov_len</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">plain_size</span><span class="p">;</span></span>
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385
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<pre style="margin: 0;">+<span id="LC385" class="line" lang="c"> <span class="n" style="color: #333;">iov</span><span class="p">[</span><span class="mi" style="color: #099;"><span class="idiff left addition">0</span></span><span class="p">].</span><span class="n" style="color: #333;">iov_base</span> <span class="o" style="font-weight: 600;">=</span> <span class="p"><span class="idiff addition">(</span></span><span class="kt" style="color: #458; font-weight: 600;"><span class="idiff addition">void</span></span><span class="idiff addition"> </span><span class="o" style="font-weight: 600;"><span class="idiff addition">*</span></span><span class="p"><span class="idiff right addition">)</span></span><span class="n" style="color: #333;">plain</span><span class="p">;</span></span>
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<td class="new_line diff-line-num new" data-linenumber="386" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#ddfbe6">
386
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<pre style="margin: 0;">+<span id="LC386" class="line" lang="c"> <span class="n" style="color: #333;">iov</span><span class="p">[</span><span class="mi" style="color: #099;"><span class="idiff left addition">0</span></span><span class="p">].</span><span class="n" style="color: #333;">iov_len</span> <span class="o" style="font-weight: 600;">=</span> <span class="p"><span class="idiff addition">(</span></span><span class="n" style="color: #333;"><span class="idiff addition">plain_size</span></span><span class="idiff addition"> </span><span class="o" style="font-weight: 600;"><span class="idiff addition">></span></span><span class="idiff addition"> </span><span class="n" style="color: #333;"><span class="idiff addition">outbuflen</span></span><span class="p"><span class="idiff addition">)</span></span><span class="idiff addition"> </span><span class="o" style="font-weight: 600;"><span class="idiff addition">?</span></span><span class="idiff addition"> </span><span class="n" style="color: #333;"><span class="idiff addition">outbuflen</span></span><span class="idiff addition"> </span><span class="o" style="font-weight: 600;"><span class="idiff addition">:</span></span><span class="idiff right addition"> </span><span class="n" style="color: #333;">plain_size</span><span class="p">;</span></span>
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387
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<pre style="margin: 0;"> <span id="LC387" class="line" lang="c"></span>
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<pre style="margin: 0;">-<span id="LC391" class="line" lang="c"> <span class="cm" style="color: #998; font-style: italic;">/* Older kernels require tag space for output. */</span></span>
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392
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<pre style="margin: 0;">-<span id="LC392" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">((</span><span class="n" style="color: #333;">auth_size</span> <span class="o" style="font-weight: 600;">+</span> <span class="n" style="color: #333;">plain_size</span><span class="p">)</span> <span class="o" style="font-weight: 600;"><</span></span>
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393
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<pre style="margin: 0;">-<span id="LC393" class="line" lang="c"> <span class="n" style="color: #333;">kcapi_aead_outbuflen_dec</span><span class="p">(</span><span class="n" style="color: #333;">ctx</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333;">handle</span><span class="p">,</span> <span class="n" style="color: #333;">plain_size</span><span class="p">,</span> <span class="n" style="color: #333;">auth_size</span><span class="p">,</span></span>
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394
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<pre style="margin: 0;">-<span id="LC394" class="line" lang="c"> <span class="n" style="color: #333;">tag_size</span><span class="p">))</span> <span class="p">{</span></span>
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<pre style="margin: 0;">-<span id="LC395" class="line" lang="c"> <span class="n" style="color: #333;">iov</span><span class="p">[</span><span class="mi" style="color: #099;">2</span><span class="p">].</span><span class="n" style="color: #333;">iov_base</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">tagtmp</span><span class="p">;</span></span>
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<pre style="margin: 0;">-<span id="LC396" class="line" lang="c"> <span class="n" style="color: #333;">iov</span><span class="p">[</span><span class="mi" style="color: #099;">2</span><span class="p">].</span><span class="n" style="color: #333;">iov_len</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">tag_size</span><span class="p">;</span></span>
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<pre style="margin: 0;">-<span id="LC397" class="line" lang="c"> <span class="n" style="color: #333;">iovlen</span> <span class="o" style="font-weight: 600;">=</span> <span class="mi" style="color: #099;">3</span><span class="p">;</span></span>
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<pre style="margin: 0;">-<span id="LC398" class="line" lang="c"> <span class="p">}</span></span>
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<pre style="margin: 0;">-<span id="LC399" class="line" lang="c"></span>
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<pre style="margin: 0;">-<span id="LC400" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span><span class="n" style="color: #333;">kcapi_aead_stream_op</span><span class="p">(</span><span class="n" style="color: #333;">ctx</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333;">handle</span><span class="p">,</span> <span class="n" style="color: #333;">iov</span><span class="p">,</span> <span class="n" style="color: #333;">iovlen</span><span class="p">)</span> <span class="o" style="font-weight: 600;"><</span> <span class="mi" style="color: #099;">0</span><span class="p">){</span></span>
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<pre style="margin: 0;">+<span id="LC388" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span><span class="n" style="color: #333;">kcapi_aead_stream_op</span><span class="p">(</span><span class="n" style="color: #333;">ctx</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333;">handle</span><span class="p">,</span> <span class="n" style="color: #333;">iov</span><span class="p">,</span> <span class="mi" style="color: #099;">1</span><span class="p">)</span> <span class="o" style="font-weight: 600;"><</span> <span class="mi" style="color: #099;">0</span><span class="p">){</span></span>
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<div style="">
<p dir="auto">The more I think about it, the more I am unsure why the old code was removed. The kernel returns AAD || CT || Tag as a data buffer. See crypto/algif_aead.c:</p>
<p dir="auto">/*
* Copy of AAD from source to destination
*
* The AAD is copied to the destination buffer without change. Even
* when user space uses an in-place cipher operation, the kernel
* will copy the data as it does not see whether such in-place operation
* is initiated.
*
* To ensure efficiency, the following implementation ensure that the
* ciphers are invoked to perform a crypto operation in-place. This
* is achieved by memory management specified as follows.
*/</p>
<p dir="auto">/*
* Decryption operation - To achieve an in-place cipher
* operation, the following SGL structure is used:
*
* TX SGL: AAD || CT || Tag
* | | ^
* | copy | | Create SGL link.
* v v |
* RX SGL: AAD || CT ----+
*/</p>
<p dir="auto">Note, the result of the RX SGL is then returned into the IOVECs provided by the caller.</p>
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