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Peter Anvin" Subject: [PATCH V2 3/3] x86/mm/pti: warn and stop when pti_clone_pagetable() is on 1G page Date: Thu, 10 Dec 2020 22:35:26 +0800 Message-Id: <20201210143527.2398-3-jiangshanlai@gmail.com> X-Mailer: git-send-email 2.19.1.6.gb485710b In-Reply-To: <20201210143527.2398-1-jiangshanlai@gmail.com> References: <0766416e-bab5-c8e7-9466-a72e965fdb8a@intel.com> <20201210143527.2398-1-jiangshanlai@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lai Jiangshan Right now, we only clone parts of the kernel image and the cpu entry area. The cpu entry area would be insane to map with 1G pages since it maps so many different kinds of pages and has *small* mappings. For the kernel image to have a 1GB area with uniform permissions seems pretty far away to practice. It would be en even more remote possibility that a large swath of it would need to be cloned for PTI. Kernel text with a non-PCID system is probably as close as we would get. I'm also not even sure we have the code to create 1GB mappings for parts of the image. In other words, no caller calls pti_clone_pagetable() on range that includes pud large page(1G) by now. If it were called in such case, there would be bugs in the caller side or other places, so it worths a warning for robustness. We also add check for pgd_large() & p4d_large() with the same reason, and pgd_large() & p4d_large() are constant 0 which just acts as the self-comment in code without any overhead. [ Many thanks to Dave Hansen for more elaborated changelog ] Signed-off-by: Lai Jiangshan --- arch/x86/mm/pti.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index cd6da1d42ba9..e8d2df072c5c 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -321,10 +321,10 @@ pti_clone_pgtable(unsigned long start, unsigned long end, break; pgd = pgd_offset_k(addr); - if (WARN_ON(pgd_none(*pgd))) + if (WARN_ON(pgd_none(*pgd) || pgd_large(*pgd))) return; p4d = p4d_offset(pgd, addr); - if (WARN_ON(p4d_none(*p4d))) + if (WARN_ON(p4d_none(*p4d) || p4d_large(*p4d))) return; pud = pud_offset(p4d, addr); @@ -333,6 +333,8 @@ pti_clone_pgtable(unsigned long start, unsigned long end, addr = round_up(addr + 1, PUD_SIZE); continue; } + if (WARN_ON(pud_large(*pud))) + return; pmd = pmd_offset(pud, addr); if (pmd_none(*pmd)) { -- 2.19.1.6.gb485710b