mirror/json-c
1
0
Fork 0
mirror of https://github.com/json-c/json-c.git synced 2026-04-08 14:59:06 +08:00
Code Issues Packages Projects Releases Wiki Activity

Merge pull request #589 from Xyene/detect-broken-rdrand

Browse Source 
Detect broken RDRAND during initialization
This commit is contained in:
Eric Hawicz
2020-05-03 21:13:48 -04:00
committed by GitHub
parent ee90110f9b 4d36b0287d
commit a555d0e2f2
1 changed files with 33 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

37
random_seed.c
View File

@@ -43,12 +43,41 @@ static void do_cpuid(int regs[], int h)
#if HAS_X86_CPUID #if HAS_X86_CPUID
static int get_rdrand_seed(void);
// Valid values are -1 (haven't tested), 0 (no), and 1 (yes).
static int _has_rdrand = -1;
static int has_rdrand(void) static int has_rdrand(void)
{ {
// CPUID.01H:ECX.RDRAND[bit 30] == 1 if (_has_rdrand == -1)
int regs[4]; {
do_cpuid(regs, 1); // CPUID.01H:ECX.RDRAND[bit 30] == 1
return (regs[2] & (1 << 30)) != 0; int regs[4];
do_cpuid(regs, 1);
if (!(regs[2] & (1 << 30)))
{
_has_rdrand = 0;
} else
{
// Some CPUs advertise RDRAND in CPUID, but return 0xFFFFFFFF
// unconditionally. To avoid locking up later, test RDRAND here. If over
// 10 trials RDRAND has returned the same value, declare it broken.
_has_rdrand = 0;
int prev = get_rdrand_seed();
for (int i = 0; i < 10; i++) {
int temp = get_rdrand_seed();
if (temp != prev) {
_has_rdrand = 1;
break;
}
prev = temp;
}
}
}
return _has_rdrand;
} }
#endif #endif