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<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_531265170">lib/accelerated/afalg.c</a>:
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<pre style="margin: 0;">+<span id="LC239" class="line" lang="c"> <span class="p">}</span></span>
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<pre style="margin: 0;">+<span id="LC240" class="line" lang="c"></span>
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<pre style="margin: 0;">+<span id="LC241" class="line" lang="c"> <span class="k" style="font-weight: 600;">return</span> <span class="mi" style="color: #099;">0</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC242" class="line" lang="c"><span class="p">}</span></span>
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<pre style="margin: 0;">+<span id="LC243" class="line" lang="c"></span>
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<pre style="margin: 0;">+<span id="LC244" class="line" lang="c"><span class="k" style="font-weight: 600;">static</span> <span class="kt" style="color: #458; font-weight: 600;">int</span> <span class="nf" style="color: #900; font-weight: 600;">afalg_aead_decrypt</span><span class="p">(</span><span class="kt" style="color: #458; font-weight: 600;">void</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">_ctx</span><span class="p">,</span></span>
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<pre style="margin: 0;">+<span id="LC245" class="line" lang="c"> <span class="k" style="font-weight: 600;">const</span> <span class="kt" style="color: #458; font-weight: 600;">void</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">nonce</span><span class="p">,</span> <span class="kt" style="color: #458; font-weight: 600;">size_t</span> <span class="n" style="color: #333;">nonce_size</span><span class="p">,</span></span>
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<pre style="margin: 0;">+<span id="LC246" class="line" lang="c"> <span class="k" style="font-weight: 600;">const</span> <span class="kt" style="color: #458; font-weight: 600;">void</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">auth</span><span class="p">,</span> <span class="kt" style="color: #458; font-weight: 600;">size_t</span> <span class="n" style="color: #333;">auth_size</span><span class="p">,</span></span>
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<pre style="margin: 0;">+<span id="LC247" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">size_t</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="LC248" class="line" lang="c"> <span class="k" style="font-weight: 600;">const</span> <span class="kt" style="color: #458; font-weight: 600;">void</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">encr</span><span class="p">,</span> <span class="kt" style="color: #458; font-weight: 600;">size_t</span> <span class="n" style="color: #333;">encr_size</span><span class="p">,</span></span>
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<pre style="margin: 0;">+<span id="LC249" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">void</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">plain</span><span class="p">,</span> <span class="kt" style="color: #458; font-weight: 600;">size_t</span> <span class="n" style="color: #333;">plain_size</span><span class="p">)</span></span>
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<pre style="margin: 0;">+<span id="LC250" class="line" lang="c"><span class="p">{</span></span>
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<pre style="margin: 0;">+<span id="LC251" class="line" lang="c"> <span class="k" style="font-weight: 600;">struct</span> <span class="n" style="color: #333;">kcapi_aead_ctx</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">ctx</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">_ctx</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC252" class="line" lang="c"> <span class="k" style="font-weight: 600;">struct</span> <span class="n" style="color: #333;">iovec</span> <span class="n" style="color: #333;">iov</span><span class="p">[</span><span class="mi" style="color: #099;">3</span><span class="p">];</span></span>
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<pre style="margin: 0;">+<span id="LC253" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">uint32_t</span> <span class="n" style="color: #333;">iovlen</span> <span class="o" style="font-weight: 600;">=</span> <span class="mi" style="color: #099;">2</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC254" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">uint8_t</span> <span class="n" style="color: #333;">authtmp</span><span class="p">[</span><span class="n" style="color: #333;">auth_size</span><span class="p">];</span></span>
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<p dir="auto">Or a combo of stack and heap?</p>
<p dir="auto">For example, we could use something like the following that I used in a kernel patch:</p>
<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true" style="background-color: #fff; font-family: monospace; font-size: 90%; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0;"><code><span id="LC1" class="line" lang="plaintext"> u8 tmpbuf[LRNG_DRNG_BLOCKSIZE] __aligned(LRNG_KCAPI_ALIGN);</span>
<span id="LC2" class="line" lang="plaintext"> u8 *tmp_large = NULL, *tmp = tmpbuf;</span>
<span id="LC3" class="line" lang="plaintext"> u32 tmplen = sizeof(tmpbuf);</span>
<span id="LC4" class="line" lang="plaintext"></span>
<span id="LC5" class="line" lang="plaintext"> /*</span>
<span id="LC6" class="line" lang="plaintext"> * Satisfy large read requests -- as the common case are smaller</span>
<span id="LC7" class="line" lang="plaintext"> * request sizes, such as 16 or 32 bytes, avoid a kmalloc overhead for</span>
<span id="LC8" class="line" lang="plaintext"> * those by using the stack variable of tmpbuf.</span>
<span id="LC9" class="line" lang="plaintext"> */</span>
<span id="LC10" class="line" lang="plaintext"> if (!CONFIG_BASE_SMALL && (nbytes > sizeof(tmpbuf))) {</span>
<span id="LC11" class="line" lang="plaintext"> tmplen = min_t(u32, nbytes, LRNG_DRNG_MAX_REQSIZE);</span>
<span id="LC12" class="line" lang="plaintext"> tmp_large = kmalloc(tmplen + LRNG_KCAPI_ALIGN, GFP_KERNEL);</span>
<span id="LC13" class="line" lang="plaintext"> if (!tmp_large)</span>
<span id="LC14" class="line" lang="plaintext"> tmplen = sizeof(tmpbuf);</span>
<span id="LC15" class="line" lang="plaintext"> else</span>
<span id="LC16" class="line" lang="plaintext"> tmp = PTR_ALIGN(tmp_large, LRNG_KCAPI_ALIGN);</span>
<span id="LC17" class="line" lang="plaintext"> }</span>
<span id="LC18" class="line" lang="plaintext">...</span>
<span id="LC19" class="line" lang="plaintext"> /* Wipe data just returned from memory */</span>
<span id="LC20" class="line" lang="plaintext"> if (tmp_large)</span>
<span id="LC21" class="line" lang="plaintext"> kfree_sensitive(tmp_large);</span>
<span id="LC22" class="line" lang="plaintext"> else</span>
<span id="LC23" class="line" lang="plaintext"> memzero_explicit(tmpbuf, sizeof(tmpbuf));</span></code></pre>
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