svn commit: r331070 - head/sys/dev/random
Conrad Meyer
cem at FreeBSD.org
Fri Mar 16 18:50:27 UTC 2018
Author: cem
Date: Fri Mar 16 18:50:26 2018
New Revision: 331070
URL: https://svnweb.freebsd.org/changeset/base/331070
Log:
random(4): Poll for signals during large reads
Occasionally poll for signals during large reads of the /dev/u?random
devices. This allows cancellation via SIGINT of accidental invocations of
very large reads. (A 2GB /dev/random read, which takes about 10 seconds on
my 2017 AMD Zen processor, can be aborted.)
I believe this behavior was intended since 2014 (r273997), just not fully
implemented.
This is motivated by a potential getrandom(2) interface that may not
explicitly forbid extremely large reads on 64-bit platforms -- even larger
than the 2GB limit imposed on devfs I/O by default. Such reads, if they are
to be allowed, should be cancellable by the user or administrator.
Reviewed by: delphij
Approved by: secteam (delphij)
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D14684
Modified:
head/sys/dev/random/randomdev.c
Modified: head/sys/dev/random/randomdev.c
==============================================================================
--- head/sys/dev/random/randomdev.c Fri Mar 16 18:16:31 2018 (r331069)
+++ head/sys/dev/random/randomdev.c Fri Mar 16 18:50:26 2018 (r331070)
@@ -130,7 +130,13 @@ READ_RANDOM_UIO(struct uio *uio, bool nonblock)
uint8_t *random_buf;
int error, spamcount;
ssize_t read_len, total_read, c;
+ /* 16 MiB takes about 0.08 s CPU time on my 2017 AMD Zen CPU */
+#define SIGCHK_PERIOD (16 * 1024 * 1024)
+ const size_t sigchk_period = SIGCHK_PERIOD;
+ CTASSERT(SIGCHK_PERIOD % PAGE_SIZE == 0);
+#undef SIGCHK_PERIOD
+
random_buf = malloc(PAGE_SIZE, M_ENTROPY, M_WAITOK);
p_random_alg_context->ra_pre_read();
error = 0;
@@ -167,11 +173,22 @@ READ_RANDOM_UIO(struct uio *uio, bool nonblock)
read_len = MIN(read_len, PAGE_SIZE);
p_random_alg_context->ra_read(random_buf, read_len);
c = MIN(uio->uio_resid, read_len);
+ /*
+ * uiomove() may yield the CPU before each 'c' bytes
+ * (up to PAGE_SIZE) are copied out.
+ */
error = uiomove(random_buf, c, uio);
total_read += c;
+ /*
+ * Poll for signals every few MBs to avoid very long
+ * uninterruptible syscalls.
+ */
+ if (error == 0 && uio->uio_resid != 0 &&
+ total_read % sigchk_period == 0)
+ error = tsleep_sbt(&random_alg_context, PCATCH,
+ "randrd", SBT_1NS, 0, C_HARDCLOCK);
}
- if (total_read != uio->uio_resid && (error == ERESTART || error == EINTR))
- /* Return partial read, not error. */
+ if (error == ERESTART || error == EINTR)
error = 0;
}
free(random_buf, M_ENTROPY);
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