[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <6e402f94fe1e942116aca729f1d54fd1399cb98a.camel@intel.com>
Date: Tue, 15 Nov 2022 20:40:19 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "peterz@...radead.org" <peterz@...radead.org>
CC: "bsingharora@...il.com" <bsingharora@...il.com>,
"hpa@...or.com" <hpa@...or.com>,
"Syromiatnikov, Eugene" <esyr@...hat.com>,
"rdunlap@...radead.org" <rdunlap@...radead.org>,
"keescook@...omium.org" <keescook@...omium.org>,
"Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
"Eranian, Stephane" <eranian@...gle.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"fweimer@...hat.com" <fweimer@...hat.com>,
"nadav.amit@...il.com" <nadav.amit@...il.com>,
"jannh@...gle.com" <jannh@...gle.com>,
"dethoma@...rosoft.com" <dethoma@...rosoft.com>,
"kcc@...gle.com" <kcc@...gle.com>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
"bp@...en8.de" <bp@...en8.de>, "oleg@...hat.com" <oleg@...hat.com>,
"hjl.tools@...il.com" <hjl.tools@...il.com>,
"Yang, Weijiang" <weijiang.yang@...el.com>,
"Lutomirski, Andy" <luto@...nel.org>,
"pavel@....cz" <pavel@....cz>, "arnd@...db.de" <arnd@...db.de>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
"x86@...nel.org" <x86@...nel.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
"john.allen@....com" <john.allen@....com>,
"rppt@...nel.org" <rppt@...nel.org>,
"mingo@...hat.com" <mingo@...hat.com>,
"Shankar, Ravi V" <ravi.v.shankar@...el.com>,
"corbet@....net" <corbet@....net>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
"gorcunov@...il.com" <gorcunov@...il.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 18/37] mm: Add guard pages around a shadow stack.
On Tue, 2022-11-15 at 13:04 +0100, Peter Zijlstra wrote:
> On Fri, Nov 04, 2022 at 03:35:45PM -0700, Rick Edgecombe wrote:
>
> > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> > index c90c20904a60..66da1f3298b0 100644
> > --- a/arch/x86/mm/mmap.c
> > +++ b/arch/x86/mm/mmap.c
> > @@ -248,3 +248,26 @@ bool pfn_modify_allowed(unsigned long pfn,
> > pgprot_t prot)
> > return false;
> > return true;
> > }
> > +
> > +unsigned long stack_guard_start_gap(struct vm_area_struct *vma)
> > +{
> > + if (vma->vm_flags & VM_GROWSDOWN)
> > + return stack_guard_gap;
> > +
> > + /*
> > + * Shadow stack pointer is moved by CALL, RET, and
> > INCSSP(Q/D).
>
> Can we perhaps write this like: INCSPP[QD] ? The () notation makes it
> look like a function.
Sure.
>
> > + * INCSSPQ moves shadow stack pointer up to 255 * 8 = ~2 KB
> > + * (~1KB for INCSSPD) and touches the first and the last
> > element
> > + * in the range, which triggers a page fault if the range is
> > not
> > + * in a shadow stack. Because of this, creating 4-KB guard
> > pages
> > + * around a shadow stack prevents these instructions from
> > going
> > + * beyond.
> > + *
> > + * Creation of VM_SHADOW_STACK is tightly controlled, so a
> > vma
> > + * can't be both VM_GROWSDOWN and VM_SHADOW_STACK
> > + */
> > + if (vma->vm_flags & VM_SHADOW_STACK)
> > + return PAGE_SIZE;
> > +
> > + return 0;
> > +}
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 5d9536fa860a..0a3f7e2b32df 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2832,15 +2832,16 @@ struct vm_area_struct *vma_lookup(struct
> > mm_struct *mm, unsigned long addr)
> > return mtree_load(&mm->mm_mt, addr);
> > }
> >
> > +unsigned long stack_guard_start_gap(struct vm_area_struct *vma);
> > +
> > static inline unsigned long vm_start_gap(struct vm_area_struct
> > *vma)
> > {
> > + unsigned long gap = stack_guard_start_gap(vma);
> > unsigned long vm_start = vma->vm_start;
> >
> > - if (vma->vm_flags & VM_GROWSDOWN) {
> > - vm_start -= stack_guard_gap;
> > - if (vm_start > vma->vm_start)
> > - vm_start = 0;
> > - }
> > + vm_start -= gap;
> > + if (vm_start > vma->vm_start)
> > + vm_start = 0;
> > return vm_start;
> > }
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 2def55555e05..f67606fbc464 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -281,6 +281,13 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
> > return origbrk;
> > }
> >
> > +unsigned long __weak stack_guard_start_gap(struct vm_area_struct
> > *vma)
> > +{
> > + if (vma->vm_flags & VM_GROWSDOWN)
> > + return stack_guard_gap;
> > + return 0;
> > +}
>
> I'm thinking perhaps this wants to be an inline function?
I don't think it can work with weak then.
Powered by blists - more mailing lists