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Mon, 13 Feb 2023 12:01:11 -0800 (PST) Date: Mon, 13 Feb 2023 12:01:09 -0800 From: Deepak Gupta To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH v1 RFC Zisslpcfi 11/20] mmu: maybe_mkwrite updated to manufacture shadow stack PTEs Message-ID: <20230213200109.GA4016181@debug.ba.rivosinc.com> References: <20230213045351.3945824-1-debug@rivosinc.com> <20230213045351.3945824-12-debug@rivosinc.com> <2d6eefb8-c7c5-7d32-9a75-ae716f828cd9@redhat.com> <20230213143754.GC3943238@debug.ba.rivosinc.com> <7693247c-a55d-a375-3621-1b07115a9d99@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <7693247c-a55d-a375-3621-1b07115a9d99@redhat.com> X-Rspam-User: X-Rspamd-Queue-Id: 6BE5A16000C X-Rspamd-Server: rspam01 X-Stat-Signature: ms7edi6tqc4wt8excxmpbfaytfydkado X-HE-Tag: 1676318473-860398 X-HE-Meta: U2FsdGVkX18z3ZwSuBeS+qXtKgFCu71jkmjqs56IpxPxjHhnxTQFM18lT+WgduwAJXYH7VVxvxkf2MiYf7UhHB6358PGwe5JcZ+YPzHDq4JmGK+RDaJqfyRadc1PQoN/1BYuySgebhjiUT5wAgtH3Hz04g6ZRh+jUhCHGIbrz5xsD5P8+Ps0PqF+CbzpWVpMxbMhPvLVIZ0ErXnOUw/Fkm76BfTy3O8iXDnXQC/Oe+ZSTJsPQ1KIB5T8RhELjrj/5lKsTlRL/AocyUnTG/ZQBAbFCpAZdZs8TuhqeklvHxY+cpWnWcGCbP3ZSgo1SpDUVHB+0HriIau+z1SJECUXlsRBTi5U8nqmTPUKEbUZiEcyLlNHF5H7lQ6g3Y24TztJ0BkWF6nrQQEi0KYB3V5fzU/HKyrQjNz8pO2jehryQrtbjL4HWey4vEvSzgP2Os0vxs12zal9Z4Uo6z0zc150RrRhh8aUyl5HLCiq0g1qs3U8AOip9mFvpjWVjSoOvD6Es0HMZOltYoFIdHXGRxEIvJFd9xSWj9FcW+IJv8iGZFjZIoaNJIejGnMtMhTyB2IhZ0lyzcozmHPJ3/19QYYZgqchpDb+jkOv/xRfqfCQ4Ww/8+r/k2e+MH61nBpTTKsugHXtZe83JX0zh0xefVGohAbmB8spUUPTIde2onmxXUEqHsRpGdY1pLFsw9Jh/ufHsldKDFI+ieAgiBiL8wIOZ29OUqBVQJM8PSC97no84Orgaqy/oy57gjVjdf/vipGvjMQY/ZcVVfzXlY1/iFs+ULvziCNI2JY3++7sfcCwHma4MA5D/WXIHwPzJsoFE4uKvO50UtvH0AKi7DScAfngwxAHqBT3MuZ7ofdoQ2bp4PpboGaPImWvYtrXg5hpE2Rej6OOI36OXz55Zi3eB4p/7EftTpZmz0MImyEpzKuV4FGwKQZfhTkmaAvYf46KzFxaZFOVQO4ghLnDN9jZlsu PXslakzT 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Feb 13, 2023 at 03:56:22PM +0100, David Hildenbrand wrote: >On 13.02.23 15:37, Deepak Gupta wrote: >>On Mon, Feb 13, 2023 at 01:05:16PM +0100, David Hildenbrand wrote: >>>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 for comment here. I looked at x86 approach. This patch >>actually written in a way which is not re-inventing wheel and is following >>a core-mm approach that fits multiple architectures. >> >>Change above checks `is_shadow_stack_vma` and if it returns true then only >>it manufactures shadow stack pte else it'll make a regular writeable mapping. >> >>Now if we look at `is_shadow_stack_vma` implementation, it returns false if >>`CONFIG_USER_SHADOW_STACK` is not defined. If `CONFIG_USER_SHADOW_STACK is >>defined then it calls `arch_is_shadow_stack_vma` which should be implemented >>by arch specific code. This allows each architecture to define their own vma >>flag encodings for shadow stack (riscv chooses presence of only `VM_WRITE` >>which is analogous to choosen PTE encodings on riscv W=1,R=0,X=0) >> >>Additionally pte_mkshdwstk will be nop if not implemented by architecture. >> >>Let me know if this make sense. If I am missing something here, let me know. > >See the discussion in that thread. The idea is to pass a VMA to >pte_mkwrite() and let it handle how to actually set it writable. > Thanks. I see. Instances where `pte_mkwrite` is directly invoked by checking VM_WRITE and thus instead of fixing all those instance, make pte_mkwrite itself take vma flag or vma. I'll revise. >-- >Thanks, > >David / dhildenb >