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Thu, 19 Jan 2023 16:03:59 +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 v2 1/2] mm: Implement memory-deny-write-execute as a prctl Date: Thu, 19 Jan 2023 16:03:43 +0000 Message-ID: <20230119160344.54358-2-joey.gouly@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20230119160344.54358-1-joey.gouly@arm.com> References: <20230119160344.54358-1-joey.gouly@arm.com> MIME-Version: 1.0 X-EOPAttributedMessage: 1 X-MS-TrafficTypeDiagnostic: AM7EUR03FT056:EE_|AS8PR08MB9528:EE_|DBAEUR03FT044:EE_|DB9PR08MB6378:EE_ X-MS-Office365-Filtering-Correlation-Id: da752411-2757-44b0-8965-08dafa36dbc3 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)(376002)(346002)(396003)(39860400002)(136003)(451199015)(40470700004)(36840700001)(46966006)(41300700001)(4326008)(6666004)(8676002)(8936002)(70206006)(70586007)(2906002)(40460700003)(36756003)(336012)(36860700001)(2616005)(82310400005)(44832011)(5660300002)(7416002)(54906003)(110136005)(316002)(40480700001)(86362001)(7696005)(186003)(478600001)(26005)(1076003)(356005)(81166007)(83380400001)(82740400003)(426003)(47076005)(17423001)(36900700001);DIR:OUT;SFP:1101; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jan 2023 16:04:34.8549 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: da752411-2757-44b0-8965-08dafa36dbc3 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: DBAEUR03FT044.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB9PR08MB6378 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230119_080441_108939_39C2556F X-CRM114-Status: GOOD ( 17.27 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 | 34 ++++++++++++++++++++++++++++++++++ include/linux/sched/coredump.h | 6 +++++- include/uapi/linux/prctl.h | 6 ++++++ kernel/sys.c | 33 +++++++++++++++++++++++++++++++++ mm/mmap.c | 10 ++++++++++ mm/mprotect.c | 5 +++++ 6 files changed, 93 insertions(+), 1 deletion(-) diff --git a/include/linux/mman.h b/include/linux/mman.h index 58b3abd457a3..cee1e4b566d8 100644 --- a/include/linux/mman.h +++ b/include/linux/mman.h @@ -156,4 +156,38 @@ calc_vm_flag_bits(unsigned long flags) } unsigned long vm_commit_limit(void); + +/* + * Denies creating a writable executable mapping or gaining executable permissions. + * + * This denies the following: + * + * a) mmap(PROT_WRITE | PROT_EXEC) + * + * b) mmap(PROT_WRITE) + * mprotect(PROT_EXEC) + * + * c) mmap(PROT_WRITE) + * mprotect(PROT_READ) + * mprotect(PROT_EXEC) + * + * But allows the following: + * + * d) mmap(PROT_READ | PROT_EXEC) + * mmap(PROT_READ | PROT_EXEC | PROT_BTI) + */ +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->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..1312a137f7fb 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_REFUSE_EXEC_GAIN 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..b3cab94545ed 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2348,6 +2348,33 @@ static int prctl_set_vma(unsigned long opt, unsigned long start, } #endif /* CONFIG_ANON_VMA_NAME */ +static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3, + unsigned long arg4, unsigned long arg5) +{ + if (arg3 || arg4 || arg5) + return -EINVAL; + + if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN)) + return -EINVAL; + + if (bits & PR_MDWE_REFUSE_EXEC_GAIN) + set_bit(MMF_HAS_MDWE, ¤t->mm->flags); + else if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags)) + return -EPERM; /* Cannot unset the flag */ + + return 0; +} + +static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3, + unsigned long arg4, unsigned long arg5) +{ + if (arg2 || arg3 || arg4 || arg5) + return -EINVAL; + + return test_bit(MMF_HAS_MDWE, ¤t->mm->flags) ? + PR_MDWE_REFUSE_EXEC_GAIN : 0; +} + SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, unsigned long, arg4, unsigned long, arg5) { @@ -2623,6 +2650,12 @@ 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(arg2, arg3, arg4, arg5); + break; + case PR_GET_MDWE: + error = prctl_get_mdwe(arg2, arg3, arg4, arg5); + 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 87d929316d57..99a4d9e2b0d8 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2665,6 +2665,16 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma_set_anonymous(vma); } + if (map_deny_write_exec(vma, vma->vm_flags)) { + error = -EACCES; + if (file) + goto close_and_free_vma; + else if (vma->vm_file) + goto unmap_and_free_vma; + else + goto free_vma; + } + /* Allow architectures to sanity-check the vm_flags */ if (!arch_validate_flags(vma->vm_flags)) { error = -EINVAL; diff --git a/mm/mprotect.c b/mm/mprotect.c index 908df12caa26..bc0587df042f 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -762,6 +762,11 @@ 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;