Re: [PATCH] IB/core: Add mitigation for Spectre V1

[Ira Weiny]

On Tue, Jul 30, 2019 at 06:52:12PM -0500, Gustavo A. R. Silva wrote:
> 
> 
> On 7/30/19 3:24 PM, Tony Luck wrote:
> > Some processors may mispredict an array bounds check and
> > speculatively access memory that they should not. With
> > a user supplied array index we like to play things safe
> > by masking the value with the array size before it is
> > used as an index.
> > 
> > Signed-off-by: Tony Luck 
> > ---
> > 
> > [I don't have h/w, so just compile tested]
> > 
> >  drivers/infiniband/core/user_mad.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/infiniband/core/user_mad.c 
> > b/drivers/infiniband/core/user_mad.c
> > index 9f8a48016b41..fdce254e4f65 100644
> > --- a/drivers/infiniband/core/user_mad.c
> > +++ b/drivers/infiniband/core/user_mad.c
> > @@ -49,6 +49,7 @@
> >  #include 
> >  #include 
> >  #include 
> > +#include 
> >  
> >  #include 
> >  
> > @@ -888,6 +889,7 @@ static int ib_umad_unreg_agent(struct ib_umad_file 
> > *file, u32 __user *arg)
> > mutex_lock(&file->port->file_mutex);
> > mutex_lock(&file->mutex);
> >  
> > +   id = array_index_nospec(id, IB_UMAD_MAX_AGENTS);
> 
> This is wrong. This prevents the below condition id >= IB_UMAD_MAX_AGENTS
> from ever being true. And I don't think this is what you want.

Ah Yea...  FWIW this would probably never be hit.

Tony; split the check?

if (id >= IB_UMAD_MAX_AGENTS) {
ret = -EINVAL;
goto out;
}

id = array_index_nospec(id, IB_UMAD_MAX_AGENTS);

if (!__get_agent(file, id)) {
ret = -EINVAL;
goto out;
}

Ira

> 
> > if (id >= IB_UMAD_MAX_AGENTS || !__get_agent(file, id)) {
> > ret = -EINVAL;
> > goto out;
> > 
> 
> --
> Gustavo

Re: [PATCH] IB/core: Add mitigation for Spectre V1

[Gustavo A. R. Silva]

On 7/30/19 3:24 PM, Tony Luck wrote:
> Some processors may mispredict an array bounds check and
> speculatively access memory that they should not. With
> a user supplied array index we like to play things safe
> by masking the value with the array size before it is
> used as an index.
> 
> Signed-off-by: Tony Luck 
> ---
> 
> [I don't have h/w, so just compile tested]
> 
>  drivers/infiniband/core/user_mad.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/infiniband/core/user_mad.c 
> b/drivers/infiniband/core/user_mad.c
> index 9f8a48016b41..fdce254e4f65 100644
> --- a/drivers/infiniband/core/user_mad.c
> +++ b/drivers/infiniband/core/user_mad.c
> @@ -49,6 +49,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  
>  #include 
>  
> @@ -888,6 +889,7 @@ static int ib_umad_unreg_agent(struct ib_umad_file *file, 
> u32 __user *arg)
>   mutex_lock(&file->port->file_mutex);
>   mutex_lock(&file->mutex);
>  
> + id = array_index_nospec(id, IB_UMAD_MAX_AGENTS);

This is wrong. This prevents the below condition id >= IB_UMAD_MAX_AGENTS
from ever being true. And I don't think this is what you want.

>   if (id >= IB_UMAD_MAX_AGENTS || !__get_agent(file, id)) {
>   ret = -EINVAL;
>   goto out;
> 

--
Gustavo

Re: [PATCH] IB/core: Add mitigation for Spectre V1

[Ira Weiny]

On Tue, Jul 30, 2019 at 01:24:07PM -0700, Tony Luck wrote:
> Some processors may mispredict an array bounds check and
> speculatively access memory that they should not. With
> a user supplied array index we like to play things safe
> by masking the value with the array size before it is
> used as an index.
> 
> Signed-off-by: Tony Luck 

Reviewed-by: Ira Weiny 
Tested-by: Ira Weiny 

> ---
> 
> [I don't have h/w, so just compile tested]
> 
>  drivers/infiniband/core/user_mad.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/infiniband/core/user_mad.c 
> b/drivers/infiniband/core/user_mad.c
> index 9f8a48016b41..fdce254e4f65 100644
> --- a/drivers/infiniband/core/user_mad.c
> +++ b/drivers/infiniband/core/user_mad.c
> @@ -49,6 +49,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  
>  #include 
>  
> @@ -888,6 +889,7 @@ static int ib_umad_unreg_agent(struct ib_umad_file *file, 
> u32 __user *arg)
>   mutex_lock(&file->port->file_mutex);
>   mutex_lock(&file->mutex);
>  
> + id = array_index_nospec(id, IB_UMAD_MAX_AGENTS);
>   if (id >= IB_UMAD_MAX_AGENTS || !__get_agent(file, id)) {
>   ret = -EINVAL;
>   goto out;
> -- 
> 2.20.1
> 

[PATCH] IB/core: Add mitigation for Spectre V1

[Tony Luck]

Some processors may mispredict an array bounds check and
speculatively access memory that they should not. With
a user supplied array index we like to play things safe
by masking the value with the array size before it is
used as an index.

Signed-off-by: Tony Luck 
---

[I don't have h/w, so just compile tested]

 drivers/infiniband/core/user_mad.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/infiniband/core/user_mad.c 
b/drivers/infiniband/core/user_mad.c
index 9f8a48016b41..fdce254e4f65 100644
--- a/drivers/infiniband/core/user_mad.c
+++ b/drivers/infiniband/core/user_mad.c
@@ -49,6 +49,7 @@
 #include 
 #include 
 #include 
+#include 
 
 #include 
 
@@ -888,6 +889,7 @@ static int ib_umad_unreg_agent(struct ib_umad_file *file, 
u32 __user *arg)
mutex_lock(&file->port->file_mutex);
mutex_lock(&file->mutex);
 
+   id = array_index_nospec(id, IB_UMAD_MAX_AGENTS);
if (id >= IB_UMAD_MAX_AGENTS || !__get_agent(file, id)) {
ret = -EINVAL;
goto out;
-- 
2.20.1