On Tue, 5 Mar 2019 17:22:41 +0900
Masami Hiramatsu <mhira...@kernel.org> wrote:
> On Tue, 5 Mar 2019 11:36:35 +0900
> Masami Hiramatsu <mhira...@kernel.org> wrote:
>
> > On Mon, 4 Mar 2019 10:59:22 -0800
> > Linus Torvalds <torva...@linux-foundation.org> wrote:
> >
> > I think the better way to do this is allowing strncpy_from_user()
> > if some conditions are match, like
> >
> > - strncpy_from_user() will be able to copy user memory with set_fs(USER_DS)
> > - strncpy_from_user() can copy kernel memory with set_fs(KERNEL_DS)
> > - strncpy_from_user() can access unsafe memory in IRQ context if
> > pagefault is disabled.
> >
> > This is almost done, except for CONFIG_DEBUG_ATOMIC_SLEEP=y on x86.
> >
> > So, what about adding a condition to WARN_ON_IN_IRQ() like below
> > instead of introducing user_access_ok() ?
OK, here is the patch. Does it work for us?
====
x86/uaccess: Verify access_ok() context strictly
From: Masami Hiramatsu <mhira...@kernel.org>
WARN_ON_IN_IRQ() assumes that the access_ok() and following
user memory access can sleep. But this assumption is not
always correct; when the pagefault is disabled, following
memory access will just returns -EFAULT and never sleep.
Add pagefault_disabled() check in WARN_ON_ONCE() so that
it can ignore the case we call it with disabling pagefault.
For this purpose, this modified pagefault_disabled() as
an inline function.
Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
---
arch/x86/include/asm/uaccess.h | 4 +++-
include/linux/uaccess.h | 5 ++++-
2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 780f2b4..b98a552 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -70,7 +70,9 @@ static inline bool __chk_range_not_ok(unsigned long addr,
unsigned long size, un
})
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
-# define WARN_ON_IN_IRQ() WARN_ON_ONCE(!in_task())
+static inline bool pagefault_disabled(void);
+# define WARN_ON_IN_IRQ() \
+ WARN_ON_ONCE(!in_task() && !pagefault_disabled())
#else
# define WARN_ON_IN_IRQ()
#endif
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 37b226e..ef3032d 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -203,7 +203,10 @@ static inline void pagefault_enable(void)
/*
* Is the pagefault handler disabled? If so, user access methods will not
sleep.
*/
-#define pagefault_disabled() (current->pagefault_disabled != 0)
+static inline bool pagefault_disabled(void)
+{
+ return current->pagefault_disabled != 0;
+}
/*
* The pagefault handler is in general disabled by pagefault_disable() or
