From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>,
Weijiang Yang <weijiang.yang@intel.com>,
Pengfei Xu <pengfei.xu@intel.com>,
Haitao Huang <haitao.huang@intel.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCH v27 12/31] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _PAGE_COW
Date: Fri, 21 May 2021 15:11:52 -0700 [thread overview]
Message-ID: <20210521221211.29077-13-yu-cheng.yu@intel.com> (raw)
In-Reply-To: <20210521221211.29077-1-yu-cheng.yu@intel.com>
When Shadow Stack is introduced, [R/O + _PAGE_DIRTY] PTE is reserved for
shadow stack. Copy-on-write PTEs have [R/O + _PAGE_COW].
When a PTE goes from [R/W + _PAGE_DIRTY] to [R/O + _PAGE_COW], it could
become a transient shadow stack PTE in two cases:
The first case is that some processors can start a write but end up seeing
a read-only PTE by the time they get to the Dirty bit, creating a transient
shadow stack PTE. However, this will not occur on processors supporting
Shadow Stack, and a TLB flush is not necessary.
The second case is that when _PAGE_DIRTY is replaced with _PAGE_COW non-
atomically, a transient shadow stack PTE can be created as a result.
Thus, prevent that with cmpxchg.
Dave Hansen, Jann Horn, Andy Lutomirski, and Peter Zijlstra provided many
insights to the issue. Jann Horn provided the cmpxchg solution.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/asm/pgtable.h | 36 ++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index f7bc20780fee..e61ad0946212 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1306,6 +1306,24 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
static inline void ptep_set_wrprotect(struct mm_struct *mm,
unsigned long addr, pte_t *ptep)
{
+ /*
+ * If Shadow Stack is enabled, pte_wrprotect() moves _PAGE_DIRTY
+ * to _PAGE_COW (see comments at pte_wrprotect()).
+ * When a thread reads a RW=1, Dirty=0 PTE and before changing it
+ * to RW=0, Dirty=0, another thread could have written to the page
+ * and the PTE is RW=1, Dirty=1 now. Use try_cmpxchg() to detect
+ * PTE changes and update old_pte, then try again.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ pte_t old_pte, new_pte;
+
+ old_pte = READ_ONCE(*ptep);
+ do {
+ new_pte = pte_wrprotect(old_pte);
+ } while (!try_cmpxchg(&ptep->pte, &old_pte.pte, new_pte.pte));
+
+ return;
+ }
clear_bit(_PAGE_BIT_RW, (unsigned long *)&ptep->pte);
}
@@ -1350,6 +1368,24 @@ static inline pud_t pudp_huge_get_and_clear(struct mm_struct *mm,
static inline void pmdp_set_wrprotect(struct mm_struct *mm,
unsigned long addr, pmd_t *pmdp)
{
+ /*
+ * If Shadow Stack is enabled, pmd_wrprotect() moves _PAGE_DIRTY
+ * to _PAGE_COW (see comments at pmd_wrprotect()).
+ * When a thread reads a RW=1, Dirty=0 PMD and before changing it
+ * to RW=0, Dirty=0, another thread could have written to the page
+ * and the PMD is RW=1, Dirty=1 now. Use try_cmpxchg() to detect
+ * PMD changes and update old_pmd, then try again.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ pmd_t old_pmd, new_pmd;
+
+ old_pmd = READ_ONCE(*pmdp);
+ do {
+ new_pmd = pmd_wrprotect(old_pmd);
+ } while (!try_cmpxchg((pmdval_t *)pmdp, (pmdval_t *)&old_pmd, pmd_val(new_pmd)));
+
+ return;
+ }
clear_bit(_PAGE_BIT_RW, (unsigned long *)pmdp);
}
--
2.21.0
next prev parent reply other threads:[~2021-05-21 22:13 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-21 22:11 [PATCH v27 00/31] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 01/31] Documentation/x86: Add CET description Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 02/31] x86/cet/shstk: Add Kconfig option for Shadow Stack Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 03/31] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 04/31] x86/cpufeatures: Introduce CPU setup and option parsing for CET Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 05/31] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 06/31] x86/cet: Add control-protection fault handler Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 07/31] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 08/31] x86/mm: Move pmd_write(), pud_write() up in the file Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 09/31] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 10/31] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 11/31] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2021-05-21 22:11 ` Yu-cheng Yu [this message]
2021-05-21 22:11 ` [PATCH v27 13/31] mm: Move VM_UFFD_MINOR_BIT from 37 to 38 Yu-cheng Yu
2021-05-21 22:25 ` Axel Rasmussen
2021-05-22 1:58 ` Yu, Yu-cheng
2021-05-21 22:11 ` [PATCH v27 14/31] mm: Introduce VM_SHADOW_STACK for shadow stack memory Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 15/31] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 16/31] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 17/31] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 18/31] mm: Add guard pages around a shadow stack Yu-cheng Yu
2021-05-21 22:11 ` [PATCH v27 19/31] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 20/31] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 21/31] mm/mprotect: Exclude shadow stack from preserve_write Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 22/31] mm: Re-introduce vm_flags to do_mmap() Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 23/31] x86/cet/shstk: Add user-mode shadow stack support Yu-cheng Yu
2021-07-19 18:23 ` Edgecombe, Rick P
2021-07-20 17:13 ` Yu, Yu-cheng
2021-05-21 22:12 ` [PATCH v27 24/31] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu
2021-05-22 23:39 ` Andy Lutomirski
2021-05-25 15:04 ` Yu, Yu-cheng
2021-07-21 18:14 ` John Allen
2021-07-21 18:28 ` Florian Weimer
2021-07-21 18:34 ` Yu, Yu-cheng
2021-07-28 21:34 ` John Allen
2021-07-21 18:37 ` Dave Hansen
2021-07-21 20:14 ` H.J. Lu
2021-05-21 22:12 ` [PATCH v27 25/31] x86/cet/shstk: Introduce shadow stack token setup/verify routines Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 26/31] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 27/31] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2021-05-25 10:54 ` Catalin Marinas
2021-05-21 22:12 ` [PATCH v27 28/31] x86/cet/shstk: Add arch_prctl functions for shadow stack Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 29/31] mm: Move arch_calc_vm_prot_bits() to arch/x86/include/asm/mman.h Yu-cheng Yu
2021-05-21 22:12 ` [PATCH v27 30/31] mm: Update arch_validate_flags() to test vma anonymous Yu-cheng Yu
2021-05-25 11:00 ` Catalin Marinas
2021-05-25 15:03 ` Yu, Yu-cheng
2021-05-21 22:12 ` [PATCH v27 31/31] mm: Introduce PROT_SHADOW_STACK for shadow stack Yu-cheng Yu
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