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Wed, 26 Oct 2022 15:05:15 +0000 From: Joey Gouly To: Catalin Marinas , Andrew Morton , Lennart Poettering , =?utf-8?q?Zbigniew_J=C4=99drze?= =?utf-8?q?jewski-Szmek?= CC: Alexander Viro , Kees Cook , Szabolcs Nagy , Mark Brown , Jeremy Linton , Topi Miettinen , , , , , , , Subject: [PATCH v1 1/2] mm: Implement memory-deny-write-execute as a prctl Date: Wed, 26 Oct 2022 16:04:56 +0100 Message-ID: <20221026150457.36957-2-joey.gouly@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20221026150457.36957-1-joey.gouly@arm.com> References: <20221026150457.36957-1-joey.gouly@arm.com> MIME-Version: 1.0 X-EOPAttributedMessage: 1 X-MS-TrafficTypeDiagnostic: DBAEUR03FT057:EE_|AM9PR08MB6692:EE_|VI1EUR03FT055:EE_|AS8PR08MB10269:EE_ X-MS-Office365-Filtering-Correlation-Id: b91ef1ea-5c64-4a4e-921b-08dab763f722 x-checkrecipientrouted: true NoDisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; X-Microsoft-Antispam-Message-Info-Original: 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 X-Forefront-Antispam-Report-Untrusted: CIP:40.67.248.234;CTRY:IE;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:nebula.arm.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230022)(4636009)(346002)(376002)(136003)(396003)(39860400002)(451199015)(40470700004)(46966006)(36840700001)(36756003)(86362001)(356005)(81166007)(82740400003)(44832011)(40460700003)(40480700001)(2906002)(2616005)(6666004)(36860700001)(83380400001)(7696005)(1076003)(26005)(336012)(478600001)(47076005)(186003)(110136005)(54906003)(426003)(82310400005)(41300700001)(316002)(70206006)(4326008)(8676002)(7416002)(5660300002)(8936002)(70586007)(17423001)(36900700001);DIR:OUT;SFP:1101; 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dkim=pass header.d=armh.onmicrosoft.com header.s=selector2-armh-onmicrosoft-com header.b=8vo6DjhP; dkim=pass header.d=armh.onmicrosoft.com header.s=selector2-armh-onmicrosoft-com header.b=8vo6DjhP; arc=pass ("microsoft.com:s=arcselector9901:i=2"); spf=pass (imf29.hostedemail.com: domain of Joey.Gouly@arm.com designates 40.107.14.89 as permitted sender) smtp.mailfrom=Joey.Gouly@arm.com; dmarc=pass (policy=none) header.from=arm.com X-Stat-Signature: u4dd4mcjwjucddz34ni8moxgmnehuxja X-Rspamd-Queue-Id: 5F727120050 X-Rspamd-Server: rspam07 X-Rspam-User: X-HE-Tag: 1666796937-193225 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: The aim of such policy is to prevent a user task from creating an executable mapping that is also writeable. An example of mmap() returning -EACCESS if the policy is enabled: mmap(0, size, PROT_READ | PROT_WRITE | PROT_EXEC, flags, 0, 0); Similarly, mprotect() would return -EACCESS below: addr = mmap(0, size, PROT_READ | PROT_EXEC, flags, 0, 0); mprotect(addr, size, PROT_READ | PROT_WRITE | PROT_EXEC); The BPF filter that systemd MDWE uses is stateless, and disallows mprotect() with PROT_EXEC completely. This new prctl allows PROT_EXEC to be enabled if it was already PROT_EXEC, which allows the following case: addr = mmap(0, size, PROT_READ | PROT_EXEC, flags, 0, 0); mprotect(addr, size, PROT_READ | PROT_EXEC | PROT_BTI); where PROT_BTI enables branch tracking identification on arm64. Signed-off-by: Joey Gouly Co-developed-by: Catalin Marinas Signed-off-by: Catalin Marinas Cc: Andrew Morton --- include/linux/mman.h | 15 +++++++++++++++ include/linux/sched/coredump.h | 6 +++++- include/uapi/linux/prctl.h | 6 ++++++ kernel/sys.c | 18 ++++++++++++++++++ mm/mmap.c | 3 +++ mm/mprotect.c | 5 +++++ 6 files changed, 52 insertions(+), 1 deletion(-) diff --git a/include/linux/mman.h b/include/linux/mman.h index 58b3abd457a3..d84fdeab6b5e 100644 --- a/include/linux/mman.h +++ b/include/linux/mman.h @@ -156,4 +156,19 @@ calc_vm_flag_bits(unsigned long flags) } unsigned long vm_commit_limit(void); + +static inline bool map_deny_write_exec(struct vm_area_struct *vma, unsigned long vm_flags) +{ + if (!test_bit(MMF_HAS_MDWE, ¤t->mm->flags)) + return false; + + if ((vm_flags & VM_EXEC) && (vm_flags & VM_WRITE)) + return true; + + if (vma && !(vma->vm_flags & VM_EXEC) && (vm_flags & VM_EXEC)) + return true; + + return false; +} + #endif /* _LINUX_MMAN_H */ diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h index 8270ad7ae14c..0e17ae7fbfd3 100644 --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -81,9 +81,13 @@ static inline int get_dumpable(struct mm_struct *mm) * lifecycle of this mm, just for simplicity. */ #define MMF_HAS_PINNED 27 /* FOLL_PIN has run, never cleared */ + +#define MMF_HAS_MDWE 28 +#define MMF_HAS_MDWE_MASK (1 << MMF_HAS_MDWE) + #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ - MMF_DISABLE_THP_MASK) + MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK) #endif /* _LINUX_SCHED_COREDUMP_H */ diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index a5e06dcbba13..ab9db1e86230 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -281,6 +281,12 @@ struct prctl_mm_map { # define PR_SME_VL_LEN_MASK 0xffff # define PR_SME_VL_INHERIT (1 << 17) /* inherit across exec */ +/* Memory deny write / execute */ +#define PR_SET_MDWE 65 +# define PR_MDWE_FLAG_MMAP 1 + +#define PR_GET_MDWE 66 + #define PR_SET_VMA 0x53564d41 # define PR_SET_VMA_ANON_NAME 0 diff --git a/kernel/sys.c b/kernel/sys.c index 5fd54bf0e886..08e1dd6d2533 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2348,6 +2348,18 @@ static int prctl_set_vma(unsigned long opt, unsigned long start, } #endif /* CONFIG_ANON_VMA_NAME */ +static inline int prctl_set_mdwe(void) +{ + set_bit(MMF_HAS_MDWE, ¤t->mm->flags); + + return 0; +} + +static inline int prctl_get_mdwe(void) +{ + return test_bit(MMF_HAS_MDWE, ¤t->mm->flags); +} + SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, unsigned long, arg4, unsigned long, arg5) { @@ -2623,6 +2635,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, error = sched_core_share_pid(arg2, arg3, arg4, arg5); break; #endif + case PR_SET_MDWE: + error = prctl_set_mdwe(); + break; + case PR_GET_MDWE: + error = prctl_get_mdwe(); + break; case PR_SET_VMA: error = prctl_set_vma(arg2, arg3, arg4, arg5); break; diff --git a/mm/mmap.c b/mm/mmap.c index 099468aee4d8..42eaf6683216 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1409,6 +1409,9 @@ unsigned long do_mmap(struct file *file, unsigned long addr, vm_flags |= VM_NORESERVE; } + if (map_deny_write_exec(NULL, vm_flags)) + return -EACCES; + addr = mmap_region(file, addr, len, vm_flags, pgoff, uf); if (!IS_ERR_VALUE(addr) && ((vm_flags & VM_LOCKED) || diff --git a/mm/mprotect.c b/mm/mprotect.c index 8d770855b591..af71ef0788fd 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -766,6 +766,11 @@ static int do_mprotect_pkey(unsigned long start, size_t len, break; } + if (map_deny_write_exec(vma, newflags)) { + error = -EACCES; + goto out; + } + /* Allow architectures to sanity-check the new flags */ if (!arch_validate_flags(newflags)) { error = -EINVAL;