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X-IronPort-AV: E=McAfee;i="6600,9927,10996"; a="14721429" X-IronPort-AV: E=Sophos;i="6.06,186,1705392000"; d="scan'208";a="14721429" Received: from fmviesa008.fm.intel.com ([10.60.135.148]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Feb 2024 11:10:05 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.06,186,1705392000"; d="scan'208";a="6911471" Received: from bdmirand-mobl.amr.corp.intel.com (HELO rpedgeco-desk4.intel.com) ([10.251.3.213]) by fmviesa008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Feb 2024 11:10:03 -0800 From: Rick Edgecombe To: Liam.Howlett@oracle.com, akpm@linux-foundation.org, debug@rivosinc.com, broonie@kernel.org, kirill.shutemov@linux.intel.com, keescook@chromium.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, luto@kernel.org, peterz@infradead.org, hpa@zytor.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: rick.p.edgecombe@intel.com Subject: [PATCH v2 8/9] x86/mm: Care about shadow stack guard gap during placement Date: Mon, 26 Feb 2024 11:09:50 -0800 Message-Id: <20240226190951.3240433-9-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240226190951.3240433-1-rick.p.edgecombe@intel.com> References: <20240226190951.3240433-1-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: DDF1D140010 X-Stat-Signature: h1at8x1aycpead6ftiezwewtwu6111io X-Rspam-User: X-HE-Tag: 1708974605-449386 X-HE-Meta: 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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: List-Subscribe: List-Unsubscribe: When memory is being placed, mmap() will take care to respect the guard gaps of certain types of memory (VM_SHADOWSTACK, VM_GROWSUP and VM_GROWSDOWN). In order to ensure guard gaps between mappings, mmap() needs to consider two things: 1. That the new mapping isn’t placed in an any existing mappings guard gaps. 2. That the new mapping isn’t placed such that any existing mappings are not in *its* guard gaps. The long standing behavior of mmap() is to ensure 1, but not take any care around 2. So for example, if there is a PAGE_SIZE free area, and a mmap() with a PAGE_SIZE size, and a type that has a guard gap is being placed, mmap() may place the shadow stack in the PAGE_SIZE free area. Then the mapping that is supposed to have a guard gap will not have a gap to the adjacent VMA. Now that the vm_flags is passed into the arch get_unmapped_area()'s, and vm_unmapped_area() is ready to consider it, have VM_SHADOW_STACK's get guard gap consideration for scenario 2. Signed-off-by: Rick Edgecombe --- arch/x86/kernel/sys_x86_64.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c index 95cb9efc47fb..f44afb3345db 100644 --- a/arch/x86/kernel/sys_x86_64.c +++ b/arch/x86/kernel/sys_x86_64.c @@ -119,6 +119,14 @@ static void find_start_end(unsigned long addr, unsigned long flags, *end = task_size_64bit(addr > DEFAULT_MAP_WINDOW); } +static inline unsigned long stack_guard_placement(vm_flags_t vm_flags) +{ + if (vm_flags & VM_SHADOW_STACK) + return PAGE_SIZE; + + return 0; +} + unsigned long arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags) @@ -150,6 +158,7 @@ arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned l info.high_limit = end; info.align_mask = 0; info.align_offset = pgoff << PAGE_SHIFT; + info.start_gap = stack_guard_placement(vm_flags); if (filp) { info.align_mask = get_align_mask(); info.align_offset += get_align_bits(); @@ -199,6 +208,7 @@ arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr0, info.low_limit = PAGE_SIZE; info.high_limit = get_mmap_base(0); + info.start_gap = stack_guard_placement(vm_flags); /* * If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area -- 2.34.1