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From: David Hildenbrand <david@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: David Hildenbrand <david@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Kees Cook <keescook@chromium.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Greg Ungerer <gerg@linux-m68k.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Mike Rapoport <rppt@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Chinwen Chang <chinwen.chang@mediatek.com>,
	Michel Lespinasse <walken@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Huang Ying <ying.huang@intel.com>, Jann Horn <jannh@google.com>,
	Feng Tang <feng.tang@intel.com>,
	Kevin Brodsky <Kevin.Brodsky@arm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Shawn Anastasio <shawn@anastas.io>,
	Steven Price <steven.price@arm.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Jens Axboe <axboe@kernel.dk>,
	Gabriel Krisman Bertazi <krisman@collabora.com>,
	Peter Xu <peterx@redhat.com>,
	Suren Baghdasaryan <surenb@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	Marco Elver <elver@google.com>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	Nicolas Viennot <Nicolas.Viennot@twosigma.com>,
	Thomas Cedeno <thomascedeno@google.com>,
	Collin Fijalkovich <cfijalkovich@google.com>,
	Michal Hocko <mhocko@suse.com>,
	linux-api@vger.kernel.org, x86@kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH RFC 4/7] binfmt: remove in-tree usage of MAP_DENYWRITE
Date: Fri, 23 Apr 2021 15:16:37 +0200	[thread overview]
Message-ID: <20210423131640.20080-5-david@redhat.com> (raw)
In-Reply-To: <20210423131640.20080-1-david@redhat.com>

At exec time when we mmap the new executable via MAP_DENYWRITE we have it
opened via do_open_execat() and already deny_write_access()'ed the file
successfully. Once exec completes, we allow_write_acces(); however,
we set mm->exe_file in begin_new_exec() via set_mm_exe_file() and
also deny_write_access() as long as mm->exe_file remains set. We'll
effectively deny write access to our executable via mm->exe_file
until mm->exe_file is changed -- when the process is removed, on new
exec, or via sys_prctl(PR_SET_MM_EXE_FILE).

Let's remove all usage of MAP_DENYWRITE, it's no longer necessary for
mm->exe_file.

In case of an elf interpreter, we'll now only deny write access to the file
during exec. This is somewhat okay, because the interpreter behaves
(and sometime is) a shared library; all shared libraries, especially the
ones loaded directly in user space like via dlopen() won't ever be mapped
via MAP_DENYWRITE, because we ignore that from user space completely;
these shared libraries can always be modified while mapped and executed.
Let's only special-case the main executable, denying write access while
being executed by a process. This can be considered a minor user space
visible change.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 arch/x86/ia32/ia32_aout.c | 6 ++----
 fs/binfmt_aout.c          | 5 ++---
 fs/binfmt_elf.c           | 4 ++--
 fs/binfmt_elf_fdpic.c     | 2 +-
 4 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index 321d7b22ad2d..9bd15241fadb 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -202,8 +202,7 @@ static int load_aout_binary(struct linux_binprm *bprm)
 
 		error = vm_mmap(bprm->file, N_TXTADDR(ex), ex.a_text,
 				PROT_READ | PROT_EXEC,
-				MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE |
-				MAP_32BIT,
+				MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
 				fd_offset);
 
 		if (error != N_TXTADDR(ex))
@@ -211,8 +210,7 @@ static int load_aout_binary(struct linux_binprm *bprm)
 
 		error = vm_mmap(bprm->file, N_DATADDR(ex), ex.a_data,
 				PROT_READ | PROT_WRITE | PROT_EXEC,
-				MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE |
-				MAP_32BIT,
+				MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
 				fd_offset + ex.a_text);
 		if (error != N_DATADDR(ex))
 			return error;
diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
index 37df8fee63d7..9c44892d6469 100644
--- a/fs/binfmt_aout.c
+++ b/fs/binfmt_aout.c
@@ -221,8 +221,7 @@ static int load_aout_binary(struct linux_binprm * bprm)
 		}
 
 		error = vm_mmap(bprm->file, N_TXTADDR(ex), ex.a_text,
-			PROT_READ | PROT_EXEC,
-			MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE;
+			PROT_READ | PROT_EXEC, MAP_FIXED | MAP_PRIVATE;
 			fd_offset);
 
 		if (error != N_TXTADDR(ex))
@@ -230,7 +229,7 @@ static int load_aout_binary(struct linux_binprm * bprm)
 
 		error = vm_mmap(bprm->file, N_DATADDR(ex), ex.a_data,
 				PROT_READ | PROT_WRITE | PROT_EXEC,
-				MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE;
+				MAP_FIXED | MAP_PRIVATE;
 				fd_offset + ex.a_text);
 		if (error != N_DATADDR(ex))
 			return error;
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 763188ac398e..76bb342e9c9b 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -622,7 +622,7 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 	eppnt = interp_elf_phdata;
 	for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++) {
 		if (eppnt->p_type == PT_LOAD) {
-			int elf_type = MAP_PRIVATE | MAP_DENYWRITE;
+			int elf_type = MAP_PRIVATE;
 			int elf_prot = make_prot(eppnt->p_flags, arch_state,
 						 true, true);
 			unsigned long vaddr = 0;
@@ -1070,7 +1070,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 		elf_prot = make_prot(elf_ppnt->p_flags, &arch_state,
 				     !!interpreter, false);
 
-		elf_flags = MAP_PRIVATE | MAP_DENYWRITE;
+		elf_flags = MAP_PRIVATE;
 
 		vaddr = elf_ppnt->p_vaddr;
 		/*
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 8723b6686b66..18a9e42e41d1 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1041,7 +1041,7 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
 		if (phdr->p_flags & PF_W) prot |= PROT_WRITE;
 		if (phdr->p_flags & PF_X) prot |= PROT_EXEC;
 
-		flags = MAP_PRIVATE | MAP_DENYWRITE;
+		flags = MAP_PRIVATE;
 		maddr = 0;
 
 		switch (params->flags & ELF_FDPIC_FLAG_ARRANGEMENT) {
-- 
2.30.2


  parent reply	other threads:[~2021-04-23 13:18 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-23 13:16 [PATCH RFC 0/7] Remove " David Hildenbrand
2021-04-23 13:16 ` [PATCH RFC 1/7] binfmt: don't use MAP_DENYWRITE when loading shared libraries via uselib() David Hildenbrand
2021-04-23 13:16 ` [PATCH RFC 2/7] kernel/fork: factor out atomcially replacing the current MM exe_file David Hildenbrand
2021-04-23 13:16 ` [PATCH RFC 3/7] kernel/fork: always deny write access to " David Hildenbrand
2021-04-23 13:16 ` David Hildenbrand [this message]
2021-04-23 13:16 ` [PATCH RFC 5/7] mm: remove VM_DENYWRITE David Hildenbrand
2021-04-23 13:16 ` [PATCH RFC 6/7] mm: ignore MAP_DENYWRITE in ksys_mmap_pgoff() David Hildenbrand
2021-04-23 13:16 ` [PATCH RFC 7/7] fs: update documentation of get_write_access() and friends David Hildenbrand

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