Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is established

[Jason Andryuk]

On Sat, Mar 31, 2018 at 2:10 PM, Boris Ostrovsky
 wrote:
> On 03/31/2018 01:38 PM, Jason Andryuk wrote:
>> On Wed, Mar 21, 2018, 5:12 PM Boris Ostrovsky > > wrote:
>>
>> On 03/19/2018 12:58 PM, Jason Andryuk wrote:
>>  > Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
>> introduced a
>>  > call to get_cpu_cap, which is fstack-protected.  This is works on
>> x86-64
>>  > as commit 4f277295e54c ("x86/xen: init %gs very early to avoid page
>>  > faults with stack protector") ensures the stack protector is
>> configured,
>>  > but it it did not cover x86-32.
>>  >
>>  > Delay calling get_cpu_cap until after xen_setup_gdt has
>> initialized the
>>  > stack canary.  Without this, a 32bit PV machine crashes early
>>  > in boot.
>>  > (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
>>  > (XEN) [ Xen-4.6.6-xc  x86_64  debug=n  Tainted:C ]
>>  > (XEN) CPU:0
>>  > (XEN) RIP:e019:[]
>>  >
>>  > And the PV kernel IP corresponds to init_scattered_cpuid_features
>>  >0xc10362f8 <+24>:mov%gs:0x14,%eax
>>  >
>>  > Fixes 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
>>  >
>>  > Signed-off-by: Jason Andryuk > >
>>  >
>>
>>
>> Applied to for-linus-4.17
>>
>>
>> Thanks. If it's not too late, can this be cc: stable?
>
> We can always try ;-)
>
> This is 4.15 and 4.16 only, I believe.

I'm using this patch on 4.14, so there as well.

-Jason

Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is established

[Boris Ostrovsky]

On 03/31/2018 01:38 PM, Jason Andryuk wrote:
On Wed, Mar 21, 2018, 5:12 PM Boris Ostrovsky 
mailto:boris.ostrov...@oracle.com>> wrote:


On 03/19/2018 12:58 PM, Jason Andryuk wrote:
 > Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
introduced a
 > call to get_cpu_cap, which is fstack-protected.  This is works on
x86-64
 > as commit 4f277295e54c ("x86/xen: init %gs very early to avoid page
 > faults with stack protector") ensures the stack protector is
configured,
 > but it it did not cover x86-32.
 >
 > Delay calling get_cpu_cap until after xen_setup_gdt has
initialized the
 > stack canary.  Without this, a 32bit PV machine crashes early
 > in boot.
 > (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
 > (XEN) [ Xen-4.6.6-xc  x86_64  debug=n  Tainted:    C ]
 > (XEN) CPU:    0
 > (XEN) RIP:    e019:[]
 >
 > And the PV kernel IP corresponds to init_scattered_cpuid_features
 >    0xc10362f8 <+24>:    mov    %gs:0x14,%eax
 >
 > Fixes 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
 >
 > Signed-off-by: Jason Andryuk mailto:jandr...@gmail.com>>
 >


Applied to for-linus-4.17


Thanks. If it's not too late, can this be cc: stable? 



We can always try ;-)

This is 4.15 and 4.16 only, I believe.

-boris



If not, I'll 
submit the request after it is in Linus's tree.


-Jason

Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is established

[Boris Ostrovsky]

On 03/19/2018 12:58 PM, Jason Andryuk wrote:
> Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings") introduced a
> call to get_cpu_cap, which is fstack-protected.  This is works on x86-64
> as commit 4f277295e54c ("x86/xen: init %gs very early to avoid page
> faults with stack protector") ensures the stack protector is configured,
> but it it did not cover x86-32.
>
> Delay calling get_cpu_cap until after xen_setup_gdt has initialized the
> stack canary.  Without this, a 32bit PV machine crashes early
> in boot.
> (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
> (XEN) [ Xen-4.6.6-xc  x86_64  debug=n  Tainted:C ]
> (XEN) CPU:0
> (XEN) RIP:e019:[]
>
> And the PV kernel IP corresponds to init_scattered_cpuid_features
>0xc10362f8 <+24>:mov%gs:0x14,%eax
>
> Fixes 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
>
> Signed-off-by: Jason Andryuk 
>


Applied to for-linus-4.17

-boris

Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is established

[Juergen Gross]

On 19/03/18 23:22, Boris Ostrovsky wrote:
> On 03/19/2018 12:58 PM, Jason Andryuk wrote:
>> Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings") introduced a
>> call to get_cpu_cap, which is fstack-protected.  This is works on x86-64
> 
> s/This is works/This works/
> 
> Reviewed-by: Boris Ostrovsky 
> 
> Do we still need 4f277295e54?

I'd rather keep it in order to avoid nasty problems in case something
changes. After all we are trying to do an initialization in C code
which should be done in assembly before entering the C part. Doing this
properly for 32-bit pv-kernels would be rather difficult, but this is no
reason to drop the correct solution for the 64-bit case.


Juergen

Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is established

[Boris Ostrovsky]

On 03/19/2018 12:58 PM, Jason Andryuk wrote:
> Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings") introduced a
> call to get_cpu_cap, which is fstack-protected.  This is works on x86-64

s/This is works/This works/

Reviewed-by: Boris Ostrovsky 

Do we still need 4f277295e54?

-boris

> as commit 4f277295e54c ("x86/xen: init %gs very early to avoid page
> faults with stack protector") ensures the stack protector is configured,
> but it it did not cover x86-32.
>
> Delay calling get_cpu_cap until after xen_setup_gdt has initialized the
> stack canary.  Without this, a 32bit PV machine crashes early
> in boot.
> (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
> (XEN) [ Xen-4.6.6-xc  x86_64  debug=n  Tainted:C ]
> (XEN) CPU:0
> (XEN) RIP:e019:[]
>
> And the PV kernel IP corresponds to init_scattered_cpuid_features
>0xc10362f8 <+24>:mov%gs:0x14,%eax
>
> Fixes 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
>
> Signed-off-by: Jason Andryuk 
> ---
>  arch/x86/xen/enlighten_pv.c | 8 
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 3c2c2530737e..c36d23aa6c35 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -1259,10 +1259,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
>*/
>   __userpte_alloc_gfp &= ~__GFP_HIGHMEM;
>  
> - /* Work out if we support NX */
> - get_cpu_cap(&boot_cpu_data);
> - x86_configure_nx();
> -
>   /* Get mfn list */
>   xen_build_dynamic_phys_to_machine();
>  
> @@ -1272,6 +1268,10 @@ asmlinkage __visible void __init xen_start_kernel(void)
>*/
>   xen_setup_gdt(0);
>  
> + /* Work out if we support NX */
> + get_cpu_cap(&boot_cpu_data);
> + x86_configure_nx();
> +
>   xen_init_irq_ops();
>  
>   /* Let's presume PV guests always boot on vCPU with id 0. */

[PATCH] x86/xen: Delay get_cpu_cap until stack canary is established

[Jason Andryuk]

Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings") introduced a
call to get_cpu_cap, which is fstack-protected.  This is works on x86-64
as commit 4f277295e54c ("x86/xen: init %gs very early to avoid page
faults with stack protector") ensures the stack protector is configured,
but it it did not cover x86-32.

Delay calling get_cpu_cap until after xen_setup_gdt has initialized the
stack canary.  Without this, a 32bit PV machine crashes early
in boot.
(XEN) Domain 0 (vcpu#0) crashed on cpu#0:
(XEN) [ Xen-4.6.6-xc  x86_64  debug=n  Tainted:C ]
(XEN) CPU:0
(XEN) RIP:e019:[]

And the PV kernel IP corresponds to init_scattered_cpuid_features
   0xc10362f8 <+24>:mov%gs:0x14,%eax

Fixes 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")

Signed-off-by: Jason Andryuk 
---
 arch/x86/xen/enlighten_pv.c | 8 
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 3c2c2530737e..c36d23aa6c35 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1259,10 +1259,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
 */
__userpte_alloc_gfp &= ~__GFP_HIGHMEM;
 
-   /* Work out if we support NX */
-   get_cpu_cap(&boot_cpu_data);
-   x86_configure_nx();
-
/* Get mfn list */
xen_build_dynamic_phys_to_machine();
 
@@ -1272,6 +1268,10 @@ asmlinkage __visible void __init xen_start_kernel(void)
 */
xen_setup_gdt(0);
 
+   /* Work out if we support NX */
+   get_cpu_cap(&boot_cpu_data);
+   x86_configure_nx();
+
xen_init_irq_ops();
 
/* Let's presume PV guests always boot on vCPU with id 0. */
-- 
2.14.3