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Tue, 04 Jul 2023 08:37:12 -0700 (PDT) Received: from revest.zrh.corp.google.com ([2a00:79e0:9d:6:99b2:81bb:8407:5369]) by smtp.gmail.com with ESMTPSA id b2-20020adfde02000000b0030c4d8930b1sm28538709wrm.91.2023.07.04.08.37.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Jul 2023 08:37:11 -0700 (PDT) From: Florent Revest To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, anshuman.khandual@arm.com, joey.gouly@arm.com, mhocko@suse.com, keescook@chromium.org, david@redhat.com, peterx@redhat.com, izbyshev@ispras.ru, broonie@kernel.org, szabolcs.nagy@arm.com, kpsingh@kernel.org, gthelen@google.com, toiwoton@gmail.com, Florent Revest Subject: [PATCH v3 4/5] mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl Date: Tue, 4 Jul 2023 17:36:28 +0200 Message-ID: <20230704153630.1591122-5-revest@chromium.org> X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog In-Reply-To: <20230704153630.1591122-1-revest@chromium.org> References: <20230704153630.1591122-1-revest@chromium.org> MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D2B671A0016 X-Stat-Signature: 1kf3panke3sngz189xisrdd7k4t817q7 X-HE-Tag: 1688485033-840385 X-HE-Meta: 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 twM2HkaD 7AhiCqzq4xgBLyBKvTC2d8BXFOjVvj3idPseae6vUvWk0/hHKQX8rQ5C9jND8OHlw0RE+URVLiRa6ASJBmi9+FGoqOBBt/XjZ8uBc9NTSgiBKgqt1BXljDCGhE+ubVdZU2YlXAf8N78mvoi4egE9ZN4JPlbPyZdyN9jJEO09T3J0ZUNpvNz5uh0o650nhx1xzTJIQrZZzhYaSGAlyl+0KDX7uCxeQKfbEeZKQzPTQcCrLeapaJZxqgHkmep+mgIZzXKxxsuB98fhnwEGGReKhYsxniIP/OcXSc8Yz4mPb/dzXkqdY59d9Mnb/hN2IAyRtmaBouCiwDoZ0vLHscgnDapv9GDmT6YixEra3F0Lj/2Fah6YgutzEYQXeSOd5HqxhAbSpoLLVmfSqu8dxJ+uVTGLQZcnECsqu/5q/YTERZ+RLw8MP/VZbQRTZY5qn5YhaHG4HOkbmCOzkGW0= 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: This extends the current PR_SET_MDWE prctl arg with a bit to indicate that the process doesn't want MDWE protection to propagate to children. To implement this no-inherit mode, the tag in current->mm->flags must be absent from MMF_INIT_MASK. This means that the encoding for "MDWE but without inherit" is different in the prctl than in the mm flags. This leads to a bit of bit-mangling in the prctl implementation. Signed-off-by: Florent Revest Reviewed-by: Kees Cook Reviewed-by: Catalin Marinas --- include/linux/sched/coredump.h | 10 ++++++++++ include/uapi/linux/prctl.h | 1 + kernel/fork.c | 2 +- kernel/sys.c | 32 ++++++++++++++++++++++++++------ tools/include/uapi/linux/prctl.h | 1 + 5 files changed, 39 insertions(+), 7 deletions(-) diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h index 0ee96ea7a0e9..1b37fa8fc723 100644 --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -91,4 +91,14 @@ static inline int get_dumpable(struct mm_struct *mm) MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK) #define MMF_VM_MERGE_ANY 29 +#define MMF_HAS_MDWE_NO_INHERIT 30 + +static inline unsigned long mmf_init_flags(unsigned long flags) +{ + if (flags & (1UL << MMF_HAS_MDWE_NO_INHERIT)) + flags &= ~((1UL << MMF_HAS_MDWE) | + (1UL << MMF_HAS_MDWE_NO_INHERIT)); + return flags & MMF_INIT_MASK; +} + #endif /* _LINUX_SCHED_COREDUMP_H */ diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index 6e9af6cbc950..dacbe824e7c3 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -284,6 +284,7 @@ struct prctl_mm_map { /* Memory deny write / execute */ #define PR_SET_MDWE 65 # define PR_MDWE_REFUSE_EXEC_GAIN (1UL << 0) +# define PR_MDWE_NO_INHERIT (1UL << 1) #define PR_GET_MDWE 66 diff --git a/kernel/fork.c b/kernel/fork.c index d17995934eb4..bc3c762d378f 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1284,7 +1284,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, hugetlb_count_init(mm); if (current->mm) { - mm->flags = current->mm->flags & MMF_INIT_MASK; + mm->flags = mmf_init_flags(current->mm->flags); mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK; } else { mm->flags = default_dump_filter; diff --git a/kernel/sys.c b/kernel/sys.c index 339fee3eff6a..1a2dc3da43ea 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2362,19 +2362,41 @@ static int prctl_set_vma(unsigned long opt, unsigned long start, } #endif /* CONFIG_ANON_VMA_NAME */ +static inline unsigned long get_current_mdwe(void) +{ + unsigned long ret = 0; + + if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags)) + ret |= PR_MDWE_REFUSE_EXEC_GAIN; + if (test_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags)) + ret |= PR_MDWE_NO_INHERIT; + + return ret; +} + static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3, unsigned long arg4, unsigned long arg5) { + unsigned long current_bits; + if (arg3 || arg4 || arg5) return -EINVAL; - if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN)) + if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT)) + return -EINVAL; + + /* NO_INHERIT only makes sense with REFUSE_EXEC_GAIN */ + if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN)) return -EINVAL; + current_bits = get_current_mdwe(); + if (current_bits && current_bits != bits) + return -EPERM; /* Cannot unset the flags */ + + if (bits & PR_MDWE_NO_INHERIT) + set_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags); 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; } @@ -2384,9 +2406,7 @@ static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3, { if (arg2 || arg3 || arg4 || arg5) return -EINVAL; - - return test_bit(MMF_HAS_MDWE, ¤t->mm->flags) ? - PR_MDWE_REFUSE_EXEC_GAIN : 0; + return (int)get_current_mdwe(); } static int prctl_get_auxv(void __user *addr, unsigned long len) diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h index 6e9af6cbc950..dacbe824e7c3 100644 --- a/tools/include/uapi/linux/prctl.h +++ b/tools/include/uapi/linux/prctl.h @@ -284,6 +284,7 @@ struct prctl_mm_map { /* Memory deny write / execute */ #define PR_SET_MDWE 65 # define PR_MDWE_REFUSE_EXEC_GAIN (1UL << 0) +# define PR_MDWE_NO_INHERIT (1UL << 1) #define PR_GET_MDWE 66