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Merge bitcoin/bitcoin#31908: Revert merge of PR #31826

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3e9b12b3e0 Revert "Merge bitcoin/bitcoin#31826: random: Check `GetRNDRRS` is supported in `InitHardwareRand` to avoid infinite loop" (Antoine Poinsot)

Pull request description:

  PR #31826 was merged [despite the code not compiling](https://github.com/bitcoin/bitcoin/pull/31826#discussion_r1961315638).

  #31902 was opened to fix the code but since this code is only targeting a not officially supported platform, we don't have a CI in place to compile and run tests on this platform, neither apparently reviewers do (nor does the author?), don't take more risk right before 29 and revert the original broken PR.

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This commit is contained in:
Ava Chow 2025-02-19 10:03:26 -08:00
commit fd14995b6a
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1 changed files with 11 additions and 34 deletions
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45
src/random.cpp
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@ -192,13 +192,11 @@ uint64_t GetRdSeed() noexcept
#elif defined(__aarch64__) && defined(HWCAP2_RNG)
bool g_rndr_supported = false;
bool g_rndrrs_supported = false;
void InitHardwareRand()
{
if (getauxval(AT_HWCAP2) & HWCAP2_RNG) {
g_rndr_supported = true;
g_rndrrs_supported = VerifyRNDRRS();
}
}
@ -206,10 +204,8 @@ 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 && g_rndrrs_supported) {
if (g_rndr_supported) {
LogPrintf("Using RNDR and RNDRRS as additional entropy sources\n");
} else if (g_rndr_supported) {
LogPrintf("Using RNDR as an additional entropy source\n");
}
}
@ -231,43 +227,24 @@ uint64_t GetRNDR() noexcept
return r1;
}
// Helper function to retrieve random value using RNDRRS
bool GetRNDRRSInternal(uint64_t &r1) noexcept
{
uint8_t ok = 0;
__asm__ volatile("mrs %0, s3_3_c2_c4_1; cset %w1, ne;"
: "=r"(r1), "=r"(ok)::"cc");
return ok != 0;
}
/** Read 64 bits of entropy using RNDRRS.
/** Read 64 bits of entropy using rndrrs.
*
* Must only be called when RNDRRS is supported.
*/
uint64_t GetRNDRRS() noexcept
{
uint8_t ok = 0;
uint64_t r1;
while (!GetRNDRRSInternal(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;
}
/** Verify if RNDRRS is supported and functional.
* Return true if it works within the retry limit.
*/
bool VerifyRNDRRS() noexcept
{
uint64_t test;
for (int retry = 0; retry < 10; ++retry) {
if (GetRNDRRSInternal(test)) {
return true;
}
__asm__ volatile("yield");
}
return false;
}
#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).
@ -318,7 +295,7 @@ void SeedHardwareSlow(CSHA512& hasher) noexcept {
return;
}
#elif defined(__aarch64__) && defined(HWCAP2_RNG)
if (g_rndrrs_supported) {
if (g_rndr_supported) {
for (int i = 0; i < 4; ++i) {
uint64_t out = GetRNDRRS();
hasher.Write((const unsigned char*)&out, sizeof(out));