Re: [PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension
* Ingo Molnar wrote:
>
> * Andy Lutomirski wrote:
>
> > The fault handling code tries to validate that a page fault from
> > user mode that would extend the stack is within a certain range of
> > the user SP. regs->sp is only equal to the user SP if
> > user_mode(regs). In the extremely unlikely event that that
> > sw_error_code had the USER bit set but the faulting instruction was
> > in the kernel (i.e. the faulting instruction was WRUSS), then the
> > *kernel* stack pointer would have been checked, which would be an
> > info leak.
> >
> > Note to -stable maintainers: don't backport this unless you backport
> > CET. The bug it fixes is unobservable in current kernels.
> >
> > Signed-off-by: Andy Lutomirski
> > ---
> > arch/x86/mm/fault.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 91d4d2722f2e..eae7ee3ce89b 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
> > bad_area(regs, sw_error_code, address);
> > return;
> > }
> > - if (sw_error_code & X86_PF_USER) {
> > + if (user_mode(regs)) {
> > /*
> > * Accessing the stack below %sp is always a bug.
> > * The large cushion allows instructions like enter
>
> Note that this check is gone now due to:
>
> 1d8ca3be86eb: x86/mm/fault: Allow stack access below %rsp
>
> Thanks,
Ok, I like your series - I have applied the first ~7 patches of it to
tip:x86/mm, the rest is interacting with 1d8ca3be86eb - will apply the
rest as well once you send a v2.
Thanks,
Ingo
Re: [PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension
* Ingo Molnar wrote:
>
> * Andy Lutomirski wrote:
>
> > The fault handling code tries to validate that a page fault from
> > user mode that would extend the stack is within a certain range of
> > the user SP. regs->sp is only equal to the user SP if
> > user_mode(regs). In the extremely unlikely event that that
> > sw_error_code had the USER bit set but the faulting instruction was
> > in the kernel (i.e. the faulting instruction was WRUSS), then the
> > *kernel* stack pointer would have been checked, which would be an
> > info leak.
> >
> > Note to -stable maintainers: don't backport this unless you backport
> > CET. The bug it fixes is unobservable in current kernels.
> >
> > Signed-off-by: Andy Lutomirski
> > ---
> > arch/x86/mm/fault.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 91d4d2722f2e..eae7ee3ce89b 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
> > bad_area(regs, sw_error_code, address);
> > return;
> > }
> > - if (sw_error_code & X86_PF_USER) {
> > + if (user_mode(regs)) {
> > /*
> > * Accessing the stack below %sp is always a bug.
> > * The large cushion allows instructions like enter
>
> Note that this check is gone now due to:
>
> 1d8ca3be86eb: x86/mm/fault: Allow stack access below %rsp
>
> Thanks,
Ok, I like your series - I have applied the first ~7 patches of it to
tip:x86/mm, the rest is interacting with 1d8ca3be86eb - will apply the
rest as well once you send a v2.
Thanks,
Ingo
Re: [PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension
* Andy Lutomirski wrote:
> The fault handling code tries to validate that a page fault from
> user mode that would extend the stack is within a certain range of
> the user SP. regs->sp is only equal to the user SP if
> user_mode(regs). In the extremely unlikely event that that
> sw_error_code had the USER bit set but the faulting instruction was
> in the kernel (i.e. the faulting instruction was WRUSS), then the
> *kernel* stack pointer would have been checked, which would be an
> info leak.
>
> Note to -stable maintainers: don't backport this unless you backport
> CET. The bug it fixes is unobservable in current kernels.
>
> Signed-off-by: Andy Lutomirski
> ---
> arch/x86/mm/fault.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 91d4d2722f2e..eae7ee3ce89b 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
> bad_area(regs, sw_error_code, address);
> return;
> }
> - if (sw_error_code & X86_PF_USER) {
> + if (user_mode(regs)) {
> /*
>* Accessing the stack below %sp is always a bug.
>* The large cushion allows instructions like enter
Note that this check is gone now due to:
1d8ca3be86eb: x86/mm/fault: Allow stack access below %rsp
Thanks,
Ingo
Re: [PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension
* Andy Lutomirski wrote:
> The fault handling code tries to validate that a page fault from
> user mode that would extend the stack is within a certain range of
> the user SP. regs->sp is only equal to the user SP if
> user_mode(regs). In the extremely unlikely event that that
> sw_error_code had the USER bit set but the faulting instruction was
> in the kernel (i.e. the faulting instruction was WRUSS), then the
> *kernel* stack pointer would have been checked, which would be an
> info leak.
>
> Note to -stable maintainers: don't backport this unless you backport
> CET. The bug it fixes is unobservable in current kernels.
>
> Signed-off-by: Andy Lutomirski
> ---
> arch/x86/mm/fault.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 91d4d2722f2e..eae7ee3ce89b 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
> bad_area(regs, sw_error_code, address);
> return;
> }
> - if (sw_error_code & X86_PF_USER) {
> + if (user_mode(regs)) {
> /*
>* Accessing the stack below %sp is always a bug.
>* The large cushion allows instructions like enter
Note that this check is gone now due to:
1d8ca3be86eb: x86/mm/fault: Allow stack access below %rsp
Thanks,
Ingo
[PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension
The fault handling code tries to validate that a page fault from
user mode that would extend the stack is within a certain range of
the user SP. regs->sp is only equal to the user SP if
user_mode(regs). In the extremely unlikely event that that
sw_error_code had the USER bit set but the faulting instruction was
in the kernel (i.e. the faulting instruction was WRUSS), then the
*kernel* stack pointer would have been checked, which would be an
info leak.
Note to -stable maintainers: don't backport this unless you backport
CET. The bug it fixes is unobservable in current kernels.
Signed-off-by: Andy Lutomirski
---
arch/x86/mm/fault.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 91d4d2722f2e..eae7ee3ce89b 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
bad_area(regs, sw_error_code, address);
return;
}
- if (sw_error_code & X86_PF_USER) {
+ if (user_mode(regs)) {
/*
* Accessing the stack below %sp is always a bug.
* The large cushion allows instructions like enter
--
2.17.2
[PATCH 02/13] x86/fault: Check user_mode(regs) when validating a stack extension
The fault handling code tries to validate that a page fault from
user mode that would extend the stack is within a certain range of
the user SP. regs->sp is only equal to the user SP if
user_mode(regs). In the extremely unlikely event that that
sw_error_code had the USER bit set but the faulting instruction was
in the kernel (i.e. the faulting instruction was WRUSS), then the
*kernel* stack pointer would have been checked, which would be an
info leak.
Note to -stable maintainers: don't backport this unless you backport
CET. The bug it fixes is unobservable in current kernels.
Signed-off-by: Andy Lutomirski
---
arch/x86/mm/fault.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 91d4d2722f2e..eae7ee3ce89b 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1377,7 +1377,7 @@ void do_user_addr_fault(struct pt_regs *regs,
bad_area(regs, sw_error_code, address);
return;
}
- if (sw_error_code & X86_PF_USER) {
+ if (user_mode(regs)) {
/*
* Accessing the stack below %sp is always a bug.
* The large cushion allows instructions like enter
--
2.17.2
