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Detect broken RDRAND during initialization.

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Some CPUs advertise RDRAND in CPUID, but return
0xFFFFFFFF unconditionally.  To avoid locking up
later, test RDRAND during initialization, and if
it returns 0xFFFFFFFF, mark it as nonexistent.

Also fix a possible segmentation fault in CPUID check.

This commit is a squashed backport of the following
commits on the master branch:

  * 0e5bbcaa16
  * 4d36b0287d
  * 8086314026
This commit is contained in:
Björn Esser
2020-05-25 13:03:31 +02:00
parent 4467e94110
commit eec4df641c
1 changed files with 49 additions and 17 deletions
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66
random_seed.c
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@@ -26,19 +26,8 @@
static void do_cpuid(int regs[], int h)
{
/* clang-format off */
__asm__ __volatile__(
#if defined __x86_64__
"pushq %%rbx;\n"
#else
"pushl %%ebx;\n"
#endif
"cpuid;\n"
#if defined __x86_64__
"popq %%rbx;\n"
#else
"popl %%ebx;\n"
#endif
: "=a"(regs[0]), [ebx] "=r"(regs[1]), "=c"(regs[2]), "=d"(regs[3])
__asm__ __volatile__("cpuid"
: "=a"(regs[0]), "=b"(regs[1]), "=c"(regs[2]), "=d"(regs[3])
: "a"(h));
/* clang-format on */
}
@@ -54,12 +43,51 @@ static void do_cpuid(int regs[], int h)
#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)
{
// CPUID.01H:ECX.RDRAND[bit 30] == 1
if (_has_rdrand != -1)
{
return _has_rdrand;
}
/* CPUID.01H:ECX.RDRAND[bit 30] == 1 */
int regs[4];
do_cpuid(regs, 1);
return (regs[2] & (1 << 30)) != 0;
if (!(regs[2] & (1 << 30)))
{
_has_rdrand = 0;
return 0;
}
/*
* Some CPUs advertise RDRAND in CPUID, but return 0xFFFFFFFF
* unconditionally. To avoid locking up later, test RDRAND here. If over
* 3 trials RDRAND has returned the same value, declare it broken.
* Example CPUs are AMD Ryzen 3000 series
* and much older AMD APUs, such as the E1-1500
* https://github.com/systemd/systemd/issues/11810
* https://linuxreviews.org/RDRAND_stops_returning_random_values_on_older_AMD_CPUs_after_suspend
*/
_has_rdrand = 0;
int prev = get_rdrand_seed();
for (int i = 0; i < 3; i++)
{
int temp = get_rdrand_seed();
if (temp != prev)
{
_has_rdrand = 1;
break;
}
prev = temp;
}
return _has_rdrand;
}
#endif
@@ -74,7 +102,7 @@ static int get_rdrand_seed(void)
{
DEBUG_SEED("get_rdrand_seed");
int _eax;
// rdrand eax
/* rdrand eax */
/* clang-format off */
__asm__ __volatile__("1: .byte 0x0F\n"
" .byte 0xC7\n"
@@ -114,7 +142,7 @@ static int get_rdrand_seed(void)
DEBUG_SEED("get_rdrand_seed");
int _eax;
retry:
// rdrand eax
/* rdrand eax */
__asm _emit 0x0F __asm _emit 0xC7 __asm _emit 0xF0
__asm jnc retry
__asm mov _eax, eax
@@ -188,6 +216,10 @@ static int get_dev_random_seed(void)
/* clang-format off */
#include <windows.h>
/* Caution: these blank lines must remain so clang-format doesn't reorder
includes to put windows.h after wincrypt.h */
#include <wincrypt.h>
/* clang-format on */
#ifndef __GNUC__