From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: [RFC PATCH v9 13/27] x86/mm: Shadow Stack page fault error checking Date: Wed, 5 Feb 2020 10:19:21 -0800 Message-ID: <20200205181935.3712-14-yu-cheng.yu@intel.com> References: <20200205181935.3712-1-yu-cheng.yu@intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20200205181935.3712-1-yu-cheng.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org To: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , 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 , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit Cc: Yu-cheng Yu List-Id: linux-api@vger.kernel.org If a page fault is triggered by a Shadow Stack (SHSTK) access (e.g. CALL/RET) or SHSTK management instructions (e.g. WRUSSQ), then bit[6] of the page fault error code is set. In access_error(), verify a SHSTK page fault is within a SHSTK memory area. It is always an error otherwise. For a valid SHSTK access, set FAULT_FLAG_WRITE to effect copy-on-write. Signed-off-by: Yu-cheng Yu --- arch/x86/include/asm/traps.h | 2 ++ arch/x86/mm/fault.c | 18 ++++++++++++++++++ 2 files changed, 20 insertions(+) diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h index 7ac26bbd0bef..8023d177fcd8 100644 --- a/arch/x86/include/asm/traps.h +++ b/arch/x86/include/asm/traps.h @@ -169,6 +169,7 @@ enum { * bit 3 == 1: use of reserved bit detected * bit 4 == 1: fault was an instruction fetch * bit 5 == 1: protection keys block access + * bit 6 == 1: shadow stack access fault */ enum x86_pf_error_code { X86_PF_PROT = 1 << 0, @@ -177,5 +178,6 @@ enum x86_pf_error_code { X86_PF_RSVD = 1 << 3, X86_PF_INSTR = 1 << 4, X86_PF_PK = 1 << 5, + X86_PF_SHSTK = 1 << 6, }; #endif /* _ASM_X86_TRAPS_H */ diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 304d31d8cbbc..9c1243302663 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1187,6 +1187,17 @@ access_error(unsigned long error_code, struct vm_area_struct *vma) (error_code & X86_PF_INSTR), foreign)) return 1; + /* + * Verify X86_PF_SHSTK is within a Shadow Stack VMA. + * It is always an error if there is a Shadow Stack + * fault outside a Shadow Stack VMA. + */ + if (error_code & X86_PF_SHSTK) { + if (!(vma->vm_flags & VM_SHSTK)) + return 1; + return 0; + } + if (error_code & X86_PF_WRITE) { /* write, present and write, not present: */ if (unlikely(!(vma->vm_flags & VM_WRITE))) @@ -1344,6 +1355,13 @@ void do_user_addr_fault(struct pt_regs *regs, perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); + /* + * If the fault is caused by a Shadow Stack access, + * i.e. CALL/RET/SAVEPREVSSP/RSTORSSP, then set + * FAULT_FLAG_WRITE to effect copy-on-write. + */ + if (hw_error_code & X86_PF_SHSTK) + flags |= FAULT_FLAG_WRITE; if (hw_error_code & X86_PF_WRITE) flags |= FAULT_FLAG_WRITE; if (hw_error_code & X86_PF_INSTR) -- 2.21.0