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Mon, 28 Aug 2023 08:09:14 -0700 (PDT) Received: from revest.zrh.corp.google.com ([2a00:79e0:9d:6:40c6:6cff:63b:c70a]) by smtp.gmail.com with ESMTPSA id v3-20020a5d43c3000000b003140fff4f75sm10730522wrr.17.2023.08.28.08.09.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Aug 2023 08:09:13 -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, ayush.jain3@amd.com, Florent Revest Subject: [PATCH v4 5/6] mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl Date: Mon, 28 Aug 2023 17:08:57 +0200 Message-ID: <20230828150858.393570-6-revest@chromium.org> X-Mailer: git-send-email 2.42.0.rc2.253.gd59a3bf2b4-goog In-Reply-To: <20230828150858.393570-1-revest@chromium.org> References: <20230828150858.393570-1-revest@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 6B8BB2002D X-Rspam-User: X-Stat-Signature: 9bupw3qpg1gno9yx68sdyprajwbmpzic X-Rspamd-Server: rspam03 X-HE-Tag: 1693235355-374027 X-HE-Meta: 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 NXw816Kd 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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: 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. Reviewed-by: Kees Cook Reviewed-by: Catalin Marinas Signed-off-by: Florent Revest --- 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 9a85c69782bd..370ed14b1ae0 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 7b8b63fb0438..9da5a1192c98 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1285,7 +1285,7 @@ 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 2410e3999ebe..4a8073c1b255 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2368,19 +2368,41 @@ 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; } @@ -2390,9 +2412,7 @@ 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 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 9a85c69782bd..370ed14b1ae0 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 -- 2.42.0.rc2.253.gd59a3bf2b4-goog