The add_early_randomness() function in drivers/char/hw_random/core.c passes
a 16-byte buffer to pseries_rng_data_read(). Unfortunately, plpar_hcall()
returns four 64-bit values and trashes 16 bytes on the stack.
This bug has been lying around for a long time. It got unveiled by:
commit d3cc7996473a7bdd33256029988ea690754e4e2a
Author: Amit Shah <[email protected]>
Date: Thu Jul 10 15:42:34 2014 +0530
hwrng: fetch randomness only after device init
It may trig a oops while loading or unloading the pseries-rng module for both
PowerVM and PowerKVM guests.
This patch does two things:
- pass an intermediate well sized buffer to plpar_hcall(). This is acceptalbe
since we're not on a hot path.
- move to the new read API so that we know the return buffer size for sure.
Signed-off-by: Greg Kurz <[email protected]>
---
Cc'ing stable as I could reproduce back to 3.15.10
drivers/char/hw_random/pseries-rng.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/char/hw_random/pseries-rng.c b/drivers/char/hw_random/pseries-rng.c
index 6226aa0..bcf86f9 100644
--- a/drivers/char/hw_random/pseries-rng.c
+++ b/drivers/char/hw_random/pseries-rng.c
@@ -25,18 +25,21 @@
#include <asm/vio.h>
-static int pseries_rng_data_read(struct hwrng *rng, u32 *data)
+static int pseries_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
+ u64 buffer[PLPAR_HCALL_BUFSIZE];
+ size_t size = max < 8 ? max : 8;
int rc;
- rc = plpar_hcall(H_RANDOM, (unsigned long *)data);
+ rc = plpar_hcall(H_RANDOM, (unsigned long *)buffer);
if (rc != H_SUCCESS) {
pr_err_ratelimited("H_RANDOM call failed %d\n", rc);
return -EIO;
}
+ memcpy(data, buffer, size);
/* The hypervisor interface returns 64 bits */
- return 8;
+ return size;
}
/**
@@ -55,7 +58,7 @@ static unsigned long pseries_rng_get_desired_dma(struct vio_dev *vdev)
static struct hwrng pseries_rng = {
.name = KBUILD_MODNAME,
- .data_read = pseries_rng_data_read,
+ .read = pseries_rng_read,
};
static int __init pseries_rng_probe(struct vio_dev *dev,
On Fri, 2014-10-31 at 07:50 +0100, Greg Kurz wrote:
> The add_early_randomness() function in drivers/char/hw_random/core.c passes
> a 16-byte buffer to pseries_rng_data_read(). Unfortunately, plpar_hcall()
> returns four 64-bit values and trashes 16 bytes on the stack.
Hmm, thanks. I thought I'd fixed that, but I guess I never sent the patch :}
> This bug has been lying around for a long time. It got unveiled by:
>
> commit d3cc7996473a7bdd33256029988ea690754e4e2a
> Author: Amit Shah <[email protected]>
> Date: Thu Jul 10 15:42:34 2014 +0530
>
> hwrng: fetch randomness only after device init
>
> It may trig a oops while loading or unloading the pseries-rng module for both
> PowerVM and PowerKVM guests.
>
> This patch does two things:
> - pass an intermediate well sized buffer to plpar_hcall(). This is acceptalbe
> since we're not on a hot path.
Well probably, can you do a before and after test of dd if=/dev/hwrng ?
> Cc'ing stable as I could reproduce back to 3.15.10
The right way to CC stable for a patch that isn't yet in upstream is to add:
CC: [email protected]
Before your Signed-off-by. They will then pick it up once it's merged into
Linus' tree. See Documentation/stable_kernel_rules.txt
cheers
On Fri, 31 Oct 2014 18:00:12 +1100
Michael Ellerman <[email protected]> wrote:
> On Fri, 2014-10-31 at 07:50 +0100, Greg Kurz wrote:
> > The add_early_randomness() function in drivers/char/hw_random/core.c passes
> > a 16-byte buffer to pseries_rng_data_read(). Unfortunately, plpar_hcall()
> > returns four 64-bit values and trashes 16 bytes on the stack.
>
> Hmm, thanks. I thought I'd fixed that, but I guess I never sent the patch :}
>
Heh so many patches ! :)
> > This bug has been lying around for a long time. It got unveiled by:
> >
> > commit d3cc7996473a7bdd33256029988ea690754e4e2a
> > Author: Amit Shah <[email protected]>
> > Date: Thu Jul 10 15:42:34 2014 +0530
> >
> > hwrng: fetch randomness only after device init
> >
> > It may trig a oops while loading or unloading the pseries-rng module for both
> > PowerVM and PowerKVM guests.
> >
> > This patch does two things:
> > - pass an intermediate well sized buffer to plpar_hcall(). This is acceptalbe
> > since we're not on a hot path.
>
> Well probably, can you do a before and after test of dd if=/dev/hwrng ?
>
I had to do this to be able to run the before test:
@@ -78,7 +78,7 @@ static size_t rng_buffer_size(void)
static void add_early_randomness(struct hwrng *rng)
{
- unsigned char bytes[16];
+ unsigned char bytes[32];
I ran tests for 128 MB and 1G several times in a PowerKVM guest on a POWER8 box.
Before:
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024 count=131072
131072+0 records in
131072+0 records out
134217728 bytes (134 MB) copied, 17.0503 s, 7.9 MB/s
real 0m17.051s
user 0m0.024s
sys 0m16.797s
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024 count=1048576
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 136.374 s, 7.9 MB/s
real 2m16.376s
user 0m0.189s
sys 2m14.367s
After:
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024 count=131072
131072+0 records in
131072+0 records out
134217728 bytes (134 MB) copied, 17.0502 s, 7.9 MB/s
real 0m17.051s
user 0m0.024s
sys 0m16.797s
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024 count=1048576
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 136.432 s, 7.9 MB/s
real 2m16.433s
user 0m0.188s
sys 2m14.370s
It shows no degradation of performance.
> > Cc'ing stable as I could reproduce back to 3.15.10
>
> The right way to CC stable for a patch that isn't yet in upstream is to add:
>
> CC: [email protected]
>
> Before your Signed-off-by. They will then pick it up once it's merged into
> Linus' tree. See Documentation/stable_kernel_rules.txt
>
> cheers
>
Oops... should I repost then ?
Thanks.
--
Greg
On Fri, Oct 31, 2014 at 10:31:41AM +0100, Greg Kurz wrote:
>
> > > Cc'ing stable as I could reproduce back to 3.15.10
> >
> > The right way to CC stable for a patch that isn't yet in upstream is to add:
> >
> > CC: [email protected]
> >
> > Before your Signed-off-by. They will then pick it up once it's merged into
> > Linus' tree. See Documentation/stable_kernel_rules.txt
> >
> > cheers
> >
>
> Oops... should I repost then ?
Don't worry, I can fix this up.
Cheers,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
On Fri, Oct 31, 2014 at 07:50:11AM +0100, Greg Kurz wrote:
> The add_early_randomness() function in drivers/char/hw_random/core.c passes
> a 16-byte buffer to pseries_rng_data_read(). Unfortunately, plpar_hcall()
> returns four 64-bit values and trashes 16 bytes on the stack.
>
> This bug has been lying around for a long time. It got unveiled by:
>
> commit d3cc7996473a7bdd33256029988ea690754e4e2a
> Author: Amit Shah <[email protected]>
> Date: Thu Jul 10 15:42:34 2014 +0530
>
> hwrng: fetch randomness only after device init
>
> It may trig a oops while loading or unloading the pseries-rng module for both
> PowerVM and PowerKVM guests.
>
> This patch does two things:
> - pass an intermediate well sized buffer to plpar_hcall(). This is acceptalbe
> since we're not on a hot path.
> - move to the new read API so that we know the return buffer size for sure.
>
> Signed-off-by: Greg Kurz <[email protected]>
Patch applied to crypto.
Thanks,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt