1. photon
  2. Commit 646f61ee2a72741bfa816a6bdf66b68b2c5bb01e
Browse code

kernels: Improve error-handling of rdrand-rng kernel driver

Improve the rdrand-rng driver to be robust in the face of various
errors and edge cases. Specifically,

- arch_get_random_long() and arch_get_random_seed_long() can fail.
Check their return values to deal with this appropriately.

- The number of random bytes requested can be arbitrary; so fill in
the supplied buffer carefully.

- Prefer rdseed over rdrand whenever possible.

Thanks to Joao Lima and Lonnie Abelbeck (@abelbeck) for suggesting
some of these improvements.

Change-Id: If1e90e683bd4aaded097859669d87ec6c423e538
Reviewed-on: http://photon-jenkins.eng.vmware.com:8082/5727
Tested-by: gerrit-photon <photon-checkins@vmware.com>
Reviewed-by: Sharath George

Srivatsa S. Bhat authored on 2018/09/19 09:04:48
Showing 3 changed files
SPECS/linux/0001-hwrng-rdrand-Add-RNG-driver-based-on-x86-rdrand-inst.patch
History View file @ 646f61e
... ... 
@@ -12,14 +12,15 @@ entropy-starved virtual machines.
12 12
13 13 
 Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
14 14 
 ---
15 
- drivers/char/hw_random/Kconfig      | 14 +++++++++
15 
+
16 
+ drivers/char/hw_random/Kconfig      | 14 ++++++++
16 17 
  drivers/char/hw_random/Makefile     |  1 +
17 
- drivers/char/hw_random/rdrand-rng.c | 61 +++++++++++++++++++++++++++++++++++++
18 
- 3 files changed, 76 insertions(+)
18 
+ drivers/char/hw_random/rdrand-rng.c | 72 +++++++++++++++++++++++++++++++++++++
19 
+ 3 files changed, 87 insertions(+)
19 20 
  create mode 100644 drivers/char/hw_random/rdrand-rng.c
20 21
21 22 
 diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
22 
-index dbf2271..b4e558d 100644
23 
+index dbf2271..32e6196 100644
23 24 
 --- a/drivers/char/hw_random/Kconfig
24 25 
 +++ b/drivers/char/hw_random/Kconfig
25 26 
 @@ -62,6 +62,20 @@ config HW_RANDOM_AMD
... ... 
@@ -32,7 +33,7 @@ index dbf2271..b4e558d 100644
32 32 
 +	default HW_RANDOM
33 33 
 +	---help---
34 34 
 +	  This driver provides kernel-side support for a Random Number
35 
-+	  Generator that uses the 'rdrand' instruction on modern Intel
35 
++	  Generator that uses the RDRAND/RDSEED instructions on modern Intel
36 36 
 +	  and AMD CPUs.
37 37 
 +
38 38 
 +	  To compile this driver as a module, choose M here: the
... ... 
@@ -57,13 +58,13 @@ index 5ad3976..c186ddb 100644
57 57 
  obj-$(CONFIG_HW_RANDOM_GEODE) += geode-rng.o
58 58 
 diff --git a/drivers/char/hw_random/rdrand-rng.c b/drivers/char/hw_random/rdrand-rng.c
59 59 
 new file mode 100644
60 
-index 0000000..e1cf7f3
60 
+index 0000000..ba017f3
61 61 
 --- /dev/null
62 62 
 +++ b/drivers/char/hw_random/rdrand-rng.c
63 
-@@ -0,0 +1,61 @@
63 
+@@ -0,0 +1,72 @@
64 64 
 +// SPDX-License-Identifier: GPL-2.0
65 65 
 +/*
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-+ * RNG driver that uses the 'rdrand' instruction (found on modern
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++ * RNG driver that uses the RDRAND/RDSEED instructions (found on modern
67 67 
 + * Intel and AMD CPUs).
68 68 
 + *
69 69 
 + * Author: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
... ... 
@@ -77,18 +78,27 @@ index 0000000..e1cf7f3
77 77 
 +
78 78 
 +#define PFX	KBUILD_MODNAME ": "
79 79 
 +
80 
-+static int rdrand_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
80 
++static int rdrand_rng_read(struct hwrng *rng, void *buf, size_t max_bytes, bool wait)
81 81 
 +{
82 
-+	unsigned long *data = buf;
83 
-+	size_t read = 0;
84 
-+
85 
-+	while (read < max) {
86 
-+		arch_get_random_long(data);
87 
-+		data++;
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-+		read += sizeof(unsigned long);
82 
++	char *p = buf;
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++	size_t read_bytes = 0;
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++
85 
++	while (max_bytes) {
86 
++		unsigned long v;
87 
++		size_t chunk = min(max_bytes, (int)sizeof(unsigned long));
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++
89 
++		if (unlikely(!arch_get_random_seed_long(&v)) &&
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++		    unlikely(!arch_get_random_long(&v))) {
91 
++			break;
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++		}
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++
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++		memcpy(p, &v, chunk);
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++		p += chunk;
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++		max_bytes -= chunk;
97 
++		read_bytes += chunk;
89 98 
 +	}
90 99 
 +
91 
-+	return read;
100 
++	return read_bytes;
92 101 
 +}
93 102 
 +
94 103 
 +static struct hwrng rdrand_rng = {
... ... 
@@ -101,8 +111,10 @@ index 0000000..e1cf7f3
101 101 
 +{
102 102 
 +	int err = -ENODEV;
103 103 
 +
104 
-+	if (!arch_has_random())
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-+		return err; /* rdrand not available. */
104 
++	if (!arch_has_random_seed() && !arch_has_random()) {
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++		pr_err(PFX "Neither RDSEED nor RDRAND is available.\n");
106 
++		return err;
107 
++	}
106 108 
 +
107 109 
 +	err = hwrng_register(&rdrand_rng);
108 110 
 +	if (err)
... ... 
@@ -120,7 +132,7 @@ index 0000000..e1cf7f3
120 120 
 +module_exit(mod_exit);
121 121 
 +
122 122 
 +MODULE_AUTHOR("Srivatsa S. Bhat <srivatsa@csail.mit.edu>");
123 
-+MODULE_DESCRIPTION("H/W RNG driver for x86 CPUs that support rdrand");
123 
++MODULE_DESCRIPTION("H/W RNG driver for x86 CPUs that support RDRAND/RDSEED");
124 124 
 +MODULE_LICENSE("GPL");
125 125 
 --
126 126 
 2.7.4
SPECS/linux/linux-esx.spec
History View file @ 646f61e
... ... 
@@ -2,7 +2,7 @@
2 2 
 Summary:       Kernel
3 3 
 Name:          linux-esx
4 4 
 Version:       4.4.153
5 
-Release:       2%{?dist}
5 
+Release:       3%{?dist}
6 6 
 License:       GPLv2
7 7 
 URL:           http://www.kernel.org/
8 8 
 Group:         System Environment/Kernel
... ... 
@@ -238,6 +238,8 @@ ln -sf linux-%{uname_r}.cfg /boot/photon.cfg
238 238 
 /usr/src/linux-headers-%{uname_r}
239 239
240 240 
 %changelog
241 
+*   Tue Sep 18 2018 Srivatsa S. Bhat <srivatsa@csail.mit.edu> 4.4.153-3
242 
+-   Improve error-handling of rdrand-rng kernel driver.
241 243 
 *   Fri Sep 07 2018 Srivatsa S. Bhat <srivatsa@csail.mit.edu> 4.4.153-2
242 244 
 -   Fix CVE-2018-13053
243 245 
 *   Tue Sep 04 2018 Srivatsa S. Bhat <srivatsa@csail.mit.edu> 4.4.153-1
SPECS/linux/linux.spec
History View file @ 646f61e
... ... 
@@ -2,7 +2,7 @@
2 2 
 Summary:        Kernel
3 3 
 Name:           linux
4 4 
 Version:    	4.4.153
5 
-Release:        2%{?kat_build:.%kat_build}%{?dist}
5 
+Release:        3%{?kat_build:.%kat_build}%{?dist}
6 6 
 License:    	GPLv2
7 7 
 URL:        	http://www.kernel.org/
8 8 
 Group:        	System Environment/Kernel
... ... 
@@ -339,6 +339,8 @@ ln -sf %{name}-%{uname_r}.cfg /boot/photon.cfg
339 339 
 /usr/share/perf-core
340 340
341 341 
 %changelog
342 
+*   Tue Sep 18 2018 Srivatsa S. Bhat <srivatsa@csail.mit.edu> 4.4.153-3
343 
+-   Improve error-handling of rdrand-rng kernel driver.
342 344 
 *   Fri Sep 07 2018 Srivatsa S. Bhat <srivatsa@csail.mit.edu> 4.4.153-2
343 345 
 -   Fix CVE-2018-13053
344 346 
 *   Tue Sep 04 2018 Srivatsa S. Bhat <srivatsa@csail.mit.edu> 4.4.153-1