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kernel: make randomread() fault reentrant

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we now access the user buffer in randomread() outside of the lock,
only copying and advancing the chacha state under the lock. this
means we can use randomread() within the fault handling path now
without fearing deadlock. this also allows multiple readers to
generate random numbers in parallel.
This commit is contained in:
cinap_lenrek 2016-09-11 02:09:07 +02:00
parent a121806126
commit 7713145638
1 changed files with 23 additions and 8 deletions
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31
sys/src/9/port/random.c
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@ -86,22 +86,37 @@ randominit(void)
}
ulong
randomread(void *xp, ulong n)
randomread(void *p, ulong n)
{
Chachastate c;
ulong b;
if(n == 0)
return 0;
if(hwrandbuf != nil)
(*hwrandbuf)(xp, n);
(*hwrandbuf)(p, n);
if(waserror()){
qunlock(rs);
nexterror();
}
/* copy chacha state and advance block counter */
qlock(rs);
chacha_encrypt((uchar*)xp, n, rs);
c = *rs;
b = rs->input[12];
rs->input[12] += (n + ChachaBsize-1)/ChachaBsize;
if(rs->input[12] < b) rs->input[13]++;
qunlock(rs);
poperror();
/* encrypt the buffer, can fault */
chacha_encrypt((uchar*)p, n, &c);
/* prevent state leakage */
memset(&c, 0, sizeof(c));
return n;
}
/* used by fastrand() */
void
genrandom(uchar *p, int n)
{
randomread(p, n);
}