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[2003:cb:c705:6d00:5870:9639:1c17:8162]) by smtp.gmail.com with ESMTPSA id y9-20020adfee09000000b002c550eb062fsm5407008wrn.14.2023.02.13.04.05.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Feb 2023 04:05:17 -0800 (PST) Message-ID: <2d6eefb8-c7c5-7d32-9a75-ae716f828cd9@redhat.com> Date: Mon, 13 Feb 2023 13:05:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v1 RFC Zisslpcfi 11/20] mmu: maybe_mkwrite updated to manufacture shadow stack PTEs Content-Language: en-US To: Deepak Gupta , linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Andrew Morton Cc: linux-mm@kvack.org References: <20230213045351.3945824-1-debug@rivosinc.com> <20230213045351.3945824-12-debug@rivosinc.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230213045351.3945824-12-debug@rivosinc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13.02.23 05:53, Deepak Gupta wrote: > maybe_mkwrite creates PTEs with WRITE encodings for underlying arch if > VM_WRITE is turned on in vma->vm_flags. Shadow stack memory is a write- > able memory except it can only be written by certain specific > instructions. This patch allows maybe_mkwrite to create shadow stack PTEs > if vma is shadow stack VMA. Each arch can define which combination of VMA > flags means a shadow stack. > > Additionally pte_mkshdwstk must be provided by arch specific PTE > construction headers to create shadow stack PTEs. (in arch specific > pgtable.h). > > This patch provides dummy/stub pte_mkshdwstk if CONFIG_USER_SHADOW_STACK > is not selected. > > Signed-off-by: Deepak Gupta > --- > include/linux/mm.h | 23 +++++++++++++++++++++-- > include/linux/pgtable.h | 4 ++++ > 2 files changed, 25 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 8f857163ac89..a7705bc49bfe 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1093,6 +1093,21 @@ static inline unsigned long thp_size(struct page *page) > void free_compound_page(struct page *page); > > #ifdef CONFIG_MMU > + > +#ifdef CONFIG_USER_SHADOW_STACK > +bool arch_is_shadow_stack_vma(struct vm_area_struct *vma); > +#endif > + > +static inline bool > +is_shadow_stack_vma(struct vm_area_struct *vma) > +{ > +#ifdef CONFIG_USER_SHADOW_STACK > + return arch_is_shadow_stack_vma(vma); > +#else > + return false; > +#endif > +} > + > /* > * Do pte_mkwrite, but only if the vma says VM_WRITE. We do this when > * servicing faults for write access. In the normal case, do always want > @@ -1101,8 +1116,12 @@ void free_compound_page(struct page *page); > */ > static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) > { > - if (likely(vma->vm_flags & VM_WRITE)) > - pte = pte_mkwrite(pte); > + if (likely(vma->vm_flags & VM_WRITE)) { > + if (unlikely(is_shadow_stack_vma(vma))) > + pte = pte_mkshdwstk(pte); > + else > + pte = pte_mkwrite(pte); > + } > return pte; Exactly what we are trying to avoid in the x86 approach right now. Please see the x86 series on details, we shouldn't try reinventing the wheel but finding a core-mm approach that fits multiple architectures. https://lkml.kernel.org/r/20230119212317.8324-1-rick.p.edgecombe@intel.com -- Thanks, David / dhildenb