Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-12 Thread Mimi Zohar
On Wed, 2018-04-11 at 16:09 -0400, Mimi Zohar wrote:
> On Wed, 2018-04-11 at 14:00 -0500, Eric W. Biederman wrote:
> > David Howells  writes:
> > 
> > > From: Matthew Garrett 
> > >
> > > The kexec_load() syscall permits the loading and execution of arbitrary
> > > code in ring 0, which is something that lock-down is meant to prevent. It
> > > makes sense to disable kexec_load() in this situation.
> > >
> > > This does not affect kexec_file_load() syscall which can check for a
> > > signature on the image to be booted.
> > 
> > Maybing I am missing it but I am not seeing anything that would require
> > kexec_file_load be configured such that it checks the loaded kernel.
> > 
> > Without that I don't see the point of disabling kexec_load.
> > 
> > Nacked-by: "Eric W. Biederman" 
> 
> The IMA "secure boot" policy requires the kexec image to be signed.
>  This call to kernel_is_locked_down() could be replaced with a call
> to security_kernel_read_file(NULL, READING_KEXEC_IMAGE).
> 
> It would be similar to the existing init_module syscall calling
> security_kernel_read_file().

David, enabling the IMA-appraisal "secure boot" policy should probably
not be dependent on lockdown either.

Mimi



Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-12 Thread Mimi Zohar
On Wed, 2018-04-11 at 16:09 -0400, Mimi Zohar wrote:
> On Wed, 2018-04-11 at 14:00 -0500, Eric W. Biederman wrote:
> > David Howells  writes:
> > 
> > > From: Matthew Garrett 
> > >
> > > The kexec_load() syscall permits the loading and execution of arbitrary
> > > code in ring 0, which is something that lock-down is meant to prevent. It
> > > makes sense to disable kexec_load() in this situation.
> > >
> > > This does not affect kexec_file_load() syscall which can check for a
> > > signature on the image to be booted.
> > 
> > Maybing I am missing it but I am not seeing anything that would require
> > kexec_file_load be configured such that it checks the loaded kernel.
> > 
> > Without that I don't see the point of disabling kexec_load.
> > 
> > Nacked-by: "Eric W. Biederman" 
> 
> The IMA "secure boot" policy requires the kexec image to be signed.
>  This call to kernel_is_locked_down() could be replaced with a call
> to security_kernel_read_file(NULL, READING_KEXEC_IMAGE).
> 
> It would be similar to the existing init_module syscall calling
> security_kernel_read_file().

David, enabling the IMA-appraisal "secure boot" policy should probably
not be dependent on lockdown either.

Mimi



Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-11 Thread Mimi Zohar
On Wed, 2018-04-11 at 14:00 -0500, Eric W. Biederman wrote:
> David Howells  writes:
> 
> > From: Matthew Garrett 
> >
> > The kexec_load() syscall permits the loading and execution of arbitrary
> > code in ring 0, which is something that lock-down is meant to prevent. It
> > makes sense to disable kexec_load() in this situation.
> >
> > This does not affect kexec_file_load() syscall which can check for a
> > signature on the image to be booted.
> 
> Maybing I am missing it but I am not seeing anything that would require
> kexec_file_load be configured such that it checks the loaded kernel.
> 
> Without that I don't see the point of disabling kexec_load.
> 
> Nacked-by: "Eric W. Biederman" 

The IMA "secure boot" policy requires the kexec image to be signed.
 This call to kernel_is_locked_down() could be replaced with a call
to security_kernel_read_file(NULL, READING_KEXEC_IMAGE).

It would be similar to the existing init_module syscall calling
security_kernel_read_file().

Mimi



Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-11 Thread Mimi Zohar
On Wed, 2018-04-11 at 14:00 -0500, Eric W. Biederman wrote:
> David Howells  writes:
> 
> > From: Matthew Garrett 
> >
> > The kexec_load() syscall permits the loading and execution of arbitrary
> > code in ring 0, which is something that lock-down is meant to prevent. It
> > makes sense to disable kexec_load() in this situation.
> >
> > This does not affect kexec_file_load() syscall which can check for a
> > signature on the image to be booted.
> 
> Maybing I am missing it but I am not seeing anything that would require
> kexec_file_load be configured such that it checks the loaded kernel.
> 
> Without that I don't see the point of disabling kexec_load.
> 
> Nacked-by: "Eric W. Biederman" 

The IMA "secure boot" policy requires the kexec image to be signed.
 This call to kernel_is_locked_down() could be replaced with a call
to security_kernel_read_file(NULL, READING_KEXEC_IMAGE).

It would be similar to the existing init_module syscall calling
security_kernel_read_file().

Mimi



Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-11 Thread David Howells
Eric W. Biederman  wrote:

> Maybing I am missing it but I am not seeing anything that would require
> kexec_file_load be configured such that it checks the loaded kernel.
> 
> Without that I don't see the point of disabling kexec_load.

I meant to remove this patch too.

David


Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-11 Thread David Howells
Eric W. Biederman  wrote:

> Maybing I am missing it but I am not seeing anything that would require
> kexec_file_load be configured such that it checks the loaded kernel.
> 
> Without that I don't see the point of disabling kexec_load.

I meant to remove this patch too.

David


Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-11 Thread Eric W. Biederman
David Howells  writes:

> From: Matthew Garrett 
>
> The kexec_load() syscall permits the loading and execution of arbitrary
> code in ring 0, which is something that lock-down is meant to prevent. It
> makes sense to disable kexec_load() in this situation.
>
> This does not affect kexec_file_load() syscall which can check for a
> signature on the image to be booted.

Maybing I am missing it but I am not seeing anything that would require
kexec_file_load be configured such that it checks the loaded kernel.

Without that I don't see the point of disabling kexec_load.

Nacked-by: "Eric W. Biederman" 


Eric




> Signed-off-by: Matthew Garrett 
> Signed-off-by: David Howells 
> Acked-by: Dave Young 
> Reviewed-by: "Lee, Chun-Yi" 
> Reviewed-by: James Morris 
> cc: ke...@lists.infradead.org
> ---
>
>  kernel/kexec.c |7 +++
>  1 file changed, 7 insertions(+)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index aed8fb2564b3..1553ac765e73 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -199,6 +199,13 @@ static inline int kexec_load_check(unsigned long 
> nr_segments,
>   if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
>   return -EPERM;
>  
> + /*
> +  * kexec can be used to circumvent module loading restrictions, so
> +  * prevent loading in that case
> +  */
> + if (kernel_is_locked_down("kexec of unsigned images"))
> + return -EPERM;
> +
>   /*
>* Verify we have a legal set of flags
>* This leaves us room for future extensions.


Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down

2018-04-11 Thread Eric W. Biederman
David Howells  writes:

> From: Matthew Garrett 
>
> The kexec_load() syscall permits the loading and execution of arbitrary
> code in ring 0, which is something that lock-down is meant to prevent. It
> makes sense to disable kexec_load() in this situation.
>
> This does not affect kexec_file_load() syscall which can check for a
> signature on the image to be booted.

Maybing I am missing it but I am not seeing anything that would require
kexec_file_load be configured such that it checks the loaded kernel.

Without that I don't see the point of disabling kexec_load.

Nacked-by: "Eric W. Biederman" 


Eric




> Signed-off-by: Matthew Garrett 
> Signed-off-by: David Howells 
> Acked-by: Dave Young 
> Reviewed-by: "Lee, Chun-Yi" 
> Reviewed-by: James Morris 
> cc: ke...@lists.infradead.org
> ---
>
>  kernel/kexec.c |7 +++
>  1 file changed, 7 insertions(+)
>
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index aed8fb2564b3..1553ac765e73 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -199,6 +199,13 @@ static inline int kexec_load_check(unsigned long 
> nr_segments,
>   if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
>   return -EPERM;
>  
> + /*
> +  * kexec can be used to circumvent module loading restrictions, so
> +  * prevent loading in that case
> +  */
> + if (kernel_is_locked_down("kexec of unsigned images"))
> + return -EPERM;
> +
>   /*
>* Verify we have a legal set of flags
>* This leaves us room for future extensions.