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util/nvmutil: add jitter to fallback_rand entropy

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Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-12 14:35:01 +00:00
parent 38c3889f67
commit f04b796dcc
1 changed files with 22 additions and 1 deletions
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util/nvmutil/nvmutil.c
+22 -1
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@@ -164,6 +164,7 @@ static void set_mac_nib(size_t mac_str_pos,
static uint16_t hextonum(char ch_s); static uint16_t hextonum(char ch_s);
static uint16_t rhex(void); static uint16_t rhex(void);
static uint16_t fallback_rand(void); static uint16_t fallback_rand(void);
static unsigned long entropy_jitter(void);
static void write_mac_part(size_t partnum); static void write_mac_part(size_t partnum);
/* /*
@@ -1034,7 +1035,8 @@ fallback_rand(void)
^ (unsigned long)tv.tv_usec ^ (unsigned long)tv.tv_usec
^ (unsigned long)getpid() ^ (unsigned long)getpid()
^ (unsigned long)&mix ^ (unsigned long)&mix
^ counter++; ^ counter++
^ entropy_jitter();
/* /*
* Stack addresses can vary between * Stack addresses can vary between
@@ -1047,6 +1049,25 @@ fallback_rand(void)
return (uint16_t)(mix & 0xf); return (uint16_t)(mix & 0xf);
} }
static unsigned long
entropy_jitter(void)
{
struct timeval a, b;
unsigned long mix = 0;
int i;
for (i = 0; i < 8; i++) {
gettimeofday(&a, NULL);
getpid();
gettimeofday(&b, NULL);
mix ^= (unsigned long)(b.tv_usec - a.tv_usec);
mix ^= (unsigned long)&mix;
}
return mix;
}
static void static void
write_mac_part(size_t partnum) write_mac_part(size_t partnum)
{ {