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:[<00000000c10362f8>]
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 <[email protected]>
---
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
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 <[email protected]>
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:[<00000000c10362f8>]
>
> 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 <[email protected]>
> ---
> 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. */
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 <[email protected]>
>
> 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
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:[<00000000c10362f8>]
>
> 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 <[email protected]>
>
Applied to for-linus-4.17
-boris
On 03/31/2018 01:38 PM, Jason Andryuk wrote:
> On Wed, Mar 21, 2018, 5:12 PM Boris Ostrovsky
> <[email protected] <mailto:[email protected]>> 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:[<00000000c10362f8>]
> >
> > 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 <[email protected]
> <mailto:[email protected]>>
> >
>
>
> 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
>
On Sat, Mar 31, 2018 at 2:10 PM, Boris Ostrovsky
<[email protected]> wrote:
> On 03/31/2018 01:38 PM, Jason Andryuk wrote:
>> On Wed, Mar 21, 2018, 5:12 PM Boris Ostrovsky <[email protected]
>> <mailto:[email protected]>> 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:[<00000000c10362f8>]
>> >
>> > 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 <[email protected]
>> <mailto:[email protected]>>
>> >
>>
>>
>> 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