Re: [PATCH] x86/sgx: Drop racy follow_pfn check
On Fri, Feb 05, 2021 at 08:43:24AM +0100, Daniel Vetter wrote: > On Fri, Feb 5, 2021 at 3:26 AM Jarkko Sakkinen wrote: > > > > On Thu, Feb 04, 2021 at 07:45:19PM +0100, Daniel Vetter wrote: > > > References: > > > https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vet...@ffwll.ch/ > > > > What is the difference between this and "Link:" anyway? > > Afaik References: is for other reading (bug reports, discussions, > other patch series), Link: is for patch submission itself (which I > think some subsystem do an entire chain of, on each revision). My > scripts aren't good enough that they add the Link: before submitting, > I add them when I apply patches (since most patches I get don't have > them anyway). > > btw since the final patch to remove follow_pfn won't be ready for 5.12 > merge window (kvm and vfio have some work to do) I think it's best if > you just queue this up in your tree? Boris has queued this to tip x86/sgx. > Thanks, Daniel > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch > /Jarkko
Re: [PATCH] x86/sgx: Drop racy follow_pfn check
On Fri, Feb 5, 2021 at 3:26 AM Jarkko Sakkinen wrote: > > On Thu, Feb 04, 2021 at 07:45:19PM +0100, Daniel Vetter wrote: > > References: > > https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vet...@ffwll.ch/ > > What is the difference between this and "Link:" anyway? Afaik References: is for other reading (bug reports, discussions, other patch series), Link: is for patch submission itself (which I think some subsystem do an entire chain of, on each revision). My scripts aren't good enough that they add the Link: before submitting, I add them when I apply patches (since most patches I get don't have them anyway). btw since the final patch to remove follow_pfn won't be ready for 5.12 merge window (kvm and vfio have some work to do) I think it's best if you just queue this up in your tree? Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
Re: [PATCH] x86/sgx: Drop racy follow_pfn check
On Thu, Feb 04, 2021 at 07:45:19PM +0100, Daniel Vetter wrote:
> PTE insertion is fundamentally racy, and this check doesn't do
> anything useful. Quoting Sean:
>
> "Yeah, it can be whacked. The original, never-upstreamed code asserted that
> the
> resolved PFN matched the PFN being installed by the fault handler as a sanity
> check on the SGX driver's EPC management. The WARN assertion got dropped for
> whatever reason, leaving that useless chunk."
Love the "whatever reason" part :-)
Shame, I was *going to* rip this off maybe around iteration v40. I have
no idea why I did not. Even backtraced years old email threads from lore.
Probably just forgot to remove it.
So, yeah, I fully agree removing it.
Reviewed-by: Jarkko Sakkinen
> Jason stumbled over this as a new user of follow_pfn, and I'm trying
> to get rid of unsafe callers of that function so it can be locked down
> further.
>
> This is independent prep work for the referenced patch series.
Apologies, consider it my bad...
/Jarkko
>
> References:
> https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vet...@ffwll.ch/
> Reported-by: Jason Gunthorpe
> Cc: Jason Gunthorpe
> Cc: Sean Christopherson
> Fixes: 947c6e11fa43 ("x86/sgx: Add ptrace() support for the SGX driver")
> Cc: Jarkko Sakkinen
> Cc: Borislav Petkov
> Cc: linux-...@vger.kernel.org
> Signed-off-by: Daniel Vetter
> ---
> arch/x86/kernel/cpu/sgx/encl.c | 8
> 1 file changed, 8 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index ee50a5010277..20a2dd5ba2b4 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -141,7 +141,6 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
> struct sgx_encl_page *entry;
> unsigned long phys_addr;
> struct sgx_encl *encl;
> - unsigned long pfn;
> vm_fault_t ret;
>
> encl = vma->vm_private_data;
> @@ -168,13 +167,6 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
>
> phys_addr = sgx_get_epc_phys_addr(entry->epc_page);
>
> - /* Check if another thread got here first to insert the PTE. */
> - if (!follow_pfn(vma, addr, )) {
> - mutex_unlock(>lock);
> -
> - return VM_FAULT_NOPAGE;
> - }
> -
> ret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr));
> if (ret != VM_FAULT_NOPAGE) {
> mutex_unlock(>lock);
> --
> 2.30.0
>
>
Re: [PATCH] x86/sgx: Drop racy follow_pfn check
On Thu, Feb 04, 2021 at 07:45:19PM +0100, Daniel Vetter wrote: > References: > https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vet...@ffwll.ch/ What is the difference between this and "Link:" anyway? /Jarkko
