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Add support for RNDR/RNDRRS for aarch64 on Linux

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This checks whether the ARMv8.5 extensions RNDR and RNDRRS
are available and uses them for random entropy purposes.

They are functionally identical to the x86 RDRAND/RDSEED
extensions and are used in a similar manner.
This commit is contained in:
John Moffett 2023-01-06 12:53:11 -05:00
parent adc41cf3b2
commit aee5404e02
1 changed files with 73 additions and 0 deletions
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73
src/random.cpp
View file

@ -40,6 +40,9 @@
#ifdef HAVE_SYSCTL_ARND
#include <sys/sysctl.h>
#endif
#if defined(HAVE_STRONG_GETAUXVAL) && defined(__aarch64__)
#include <sys/auxv.h>
#endif
[[noreturn]] static void RandFailure()
{
@ -175,6 +178,62 @@ static uint64_t GetRdSeed() noexcept
#endif
}
#elif defined(__aarch64__) && defined(HWCAP2_RNG)
static bool g_rndr_supported = false;
static void InitHardwareRand()
{
if (getauxval(AT_HWCAP2) & HWCAP2_RNG) {
g_rndr_supported = true;
}
}
static void ReportHardwareRand()
{
// This must be done in a separate function, as InitHardwareRand() may be indirectly called
// from global constructors, before logging is initialized.
if (g_rndr_supported) {
LogPrintf("Using RNDR and RNDRRS as additional entropy sources\n");
}
}
/** Read 64 bits of entropy using rndr.
*
* Must only be called when RNDR is supported.
*/
static uint64_t GetRNDR() noexcept
{
uint8_t ok;
uint64_t r1;
do {
// https://developer.arm.com/documentation/ddi0601/2022-12/AArch64-Registers/RNDR--Random-Number
__asm__ volatile("mrs %0, s3_3_c2_c4_0; cset %w1, ne;"
: "=r"(r1), "=r"(ok)::"cc");
if (ok) break;
__asm__ volatile("yield");
} while (true);
return r1;
}
/** Read 64 bits of entropy using rndrrs.
*
* Must only be called when RNDRRS is supported.
*/
static uint64_t GetRNDRRS() noexcept
{
uint8_t ok;
uint64_t r1;
do {
// https://developer.arm.com/documentation/ddi0601/2022-12/AArch64-Registers/RNDRRS--Reseeded-Random-Number
__asm__ volatile("mrs %0, s3_3_c2_c4_1; cset %w1, ne;"
: "=r"(r1), "=r"(ok)::"cc");
if (ok) break;
__asm__ volatile("yield");
} while (true);
return r1;
}
#else
/* Access to other hardware random number generators could be added here later,
* assuming it is sufficiently fast (in the order of a few hundred CPU cycles).
@ -193,6 +252,12 @@ static void SeedHardwareFast(CSHA512& hasher) noexcept {
hasher.Write((const unsigned char*)&out, sizeof(out));
return;
}
#elif defined(__aarch64__) && defined(HWCAP2_RNG)
if (g_rndr_supported) {
uint64_t out = GetRNDR();
hasher.Write((const unsigned char*)&out, sizeof(out));
return;
}
#endif
}
@ -218,6 +283,14 @@ static void SeedHardwareSlow(CSHA512& hasher) noexcept {
}
return;
}
#elif defined(__aarch64__) && defined(HWCAP2_RNG)
if (g_rndr_supported) {
for (int i = 0; i < 4; ++i) {
uint64_t out = GetRNDRRS();
hasher.Write((const unsigned char*)&out, sizeof(out));
}
return;
}
#endif
}