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/*
* Enable the PSTATE.DIT flag in AArch64, if available.
*
* This guarantees that data-processing instructions (or rather, a
* long list of specific ones) will have data-independent timing
* (hence the name). In other words, you want to turn this bit on if
* you're trying to do constant-time crypto.
*
* For maximum performance you'd want to turn this bit back off when
* doing any CPU-intensive stuff that _isn't_ cryptographic. That
* seems like a small concern in this code base, and carries the risk
* of losing track of whether it was on or not, so here we just enable
* it for the whole process. That's why there's only an enable_dit()
* function in this file and not a disable_dit() to go with it.
*/
#include "ssh.h"
void enable_dit(void)
{
if (!platform_dit_available())
return;
asm volatile("msr dit, %0" :: "r"(1));
}
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