linux-kernel - [RFC PATCH 1/4] uaccess: Make sure kernel_uaccess_faults

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Date:   Mon, 25 Feb 2019 23:05:11 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     mhiramat@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Changbin Du <changbin.du@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Nadav Amit <namit@...are.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [RFC PATCH 1/4] uaccess: Make sure kernel_uaccess_faults_ok is updated before pagefault

Make sure the kernel_uaccess_faults_ok is updated before a
pagefault can hit and the last loads/stores issued before
resotring kernel_uaccess_faults_ok.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 fs/namespace.c |    2 ++
 mm/maccess.c   |   12 ++++++------
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index a677b59efd74..88a8e0eb6234 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2699,6 +2699,7 @@ static long exact_copy_from_user(void *to, const void __user * from,
 		return n;
 
 	current->kernel_uaccess_faults_ok++;
+	barrier();
 	while (n) {
 		if (__get_user(c, f)) {
 			memset(t, 0, n);
@@ -2708,6 +2709,7 @@ static long exact_copy_from_user(void *to, const void __user * from,
 		f++;
 		n--;
 	}
+	barrier();
 	current->kernel_uaccess_faults_ok--;
 	return n;
 }
diff --git a/mm/maccess.c b/mm/maccess.c
index f3416632e5a4..7a9752d59587 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -29,12 +29,12 @@ long __probe_kernel_read(void *dst, const void *src, size_t size)
 	mm_segment_t old_fs = get_fs();
 
 	set_fs(KERNEL_DS);
-	pagefault_disable();
 	current->kernel_uaccess_faults_ok++;
+	pagefault_disable();
 	ret = __copy_from_user_inatomic(dst,
 			(__force const void __user *)src, size);
-	current->kernel_uaccess_faults_ok--;
 	pagefault_enable();
+	current->kernel_uaccess_faults_ok--;
 	set_fs(old_fs);
 
 	return ret ? -EFAULT : 0;
@@ -59,11 +59,11 @@ long __probe_kernel_write(void *dst, const void *src, size_t size)
 	mm_segment_t old_fs = get_fs();
 
 	set_fs(KERNEL_DS);
-	pagefault_disable();
 	current->kernel_uaccess_faults_ok++;
+	pagefault_disable();
 	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
-	current->kernel_uaccess_faults_ok--;
 	pagefault_enable();
+	current->kernel_uaccess_faults_ok--;
 	set_fs(old_fs);
 
 	return ret ? -EFAULT : 0;
@@ -97,16 +97,16 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
 		return 0;
 
 	set_fs(KERNEL_DS);
-	pagefault_disable();
 	current->kernel_uaccess_faults_ok++;
+	pagefault_disable();
 
 	do {
 		ret = __get_user(*dst++, (const char __user __force *)src++);
 	} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
 
-	current->kernel_uaccess_faults_ok--;
 	dst[-1] = '\0';
 	pagefault_enable();
+	current->kernel_uaccess_faults_ok--;
 	set_fs(old_fs);
 
 	return ret ? -EFAULT : src - unsafe_addr;