| Message ID | 20210204184519.2809313-1-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86/sgx: Drop racy follow_pfn check | expand |
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 <jarkko@kernel.org> > 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.vetter@ffwll.ch/ > Reported-by: Jason Gunthorpe <jgg@ziepe.ca> > Cc: Jason Gunthorpe <jgg@ziepe.ca> > Cc: Sean Christopherson <seanjc@google.com> > Fixes: 947c6e11fa43 ("x86/sgx: Add ptrace() support for the SGX driver") > Cc: Jarkko Sakkinen <jarkko@kernel.org> > Cc: Borislav Petkov <bp@suse.de> > Cc: linux-sgx@vger.kernel.org > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > --- > 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, &pfn)) { > - mutex_unlock(&encl->lock); > - > - return VM_FAULT_NOPAGE; > - } > - > ret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr)); > if (ret != VM_FAULT_NOPAGE) { > mutex_unlock(&encl->lock); > -- > 2.30.0 > >
On Thu, Feb 04, 2021 at 07:45:19PM +0100, Daniel Vetter wrote:
> References: https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vetter@ffwll.ch/
What is the difference between this and "Link:" anyway?
/Jarkko
On Fri, Feb 5, 2021 at 3:26 AM Jarkko Sakkinen <jarkko@kernel.org> 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.vetter@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
On Fri, Feb 05, 2021 at 08:43:24AM +0100, Daniel Vetter wrote: > On Fri, Feb 5, 2021 at 3:26 AM Jarkko Sakkinen <jarkko@kernel.org> 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.vetter@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
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, &pfn)) { - mutex_unlock(&encl->lock); - - return VM_FAULT_NOPAGE; - } - ret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr)); if (ret != VM_FAULT_NOPAGE) { mutex_unlock(&encl->lock);
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." 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. References: https://lore.kernel.org/dri-devel/20201127164131.2244124-1-daniel.vetter@ffwll.ch/ Reported-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Sean Christopherson <seanjc@google.com> Fixes: 947c6e11fa43 ("x86/sgx: Add ptrace() support for the SGX driver") Cc: Jarkko Sakkinen <jarkko@kernel.org> Cc: Borislav Petkov <bp@suse.de> Cc: linux-sgx@vger.kernel.org Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> --- arch/x86/kernel/cpu/sgx/encl.c | 8 -------- 1 file changed, 8 deletions(-)