[PATCH 5.19 021/101] x86/uaccess: avoid check_object_size() in copy_from_user_nmi()

From: Greg Kroah-Hartman
Date: Mon Oct 03 2022 - 03:18:10 EST

From: Kees Cook <keescook@xxxxxxxxxxxx>

commit 59298997df89e19aad426d4ae0a7e5037074da5a upstream.

The check_object_size() helper under CONFIG_HARDENED_USERCOPY is designed
to skip any checks where the length is known at compile time as a
reasonable heuristic to avoid "likely known-good" cases. However, it can
only do this when the copy_*_user() helpers are, themselves, inline too.

Using find_vmap_area() requires taking a spinlock. The
check_object_size() helper can call find_vmap_area() when the destination
is in vmap memory. If show_regs() is called in interrupt context, it will
attempt a call to copy_from_user_nmi(), which may call check_object_size()
and then find_vmap_area(). If something in normal context happens to be
in the middle of calling find_vmap_area() (with the spinlock held), the
interrupt handler will hang forever.

The copy_from_user_nmi() call is actually being called with a fixed-size
length, so check_object_size() should never have been called in the first
place. Given the narrow constraints, just replace the
__copy_from_user_inatomic() call with an open-coded version that calls
only into the sanitizers and not check_object_size(), followed by a call
to raw_copy_from_user().

[akpm@xxxxxxxxxxxxxxxxxxxx: no instrument_copy_from_user() in my tree...]
Link: https://lkml.kernel.org/r/20220919201648.2250764-1-keescook@xxxxxxxxxxxx
Link: https://lore.kernel.org/all/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@xxxxxxxxxxxxxx
Fixes: 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reported-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Reported-by: Florian Lehner <dev@xxxxxxxxxxx>
Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Florian Lehner <dev@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
arch/x86/lib/usercopy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index ad0139d25401..f1bb18617156 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -44,7 +44,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
* called from other contexts.
- ret = __copy_from_user_inatomic(to, from, n);
+ ret = raw_copy_from_user(to, from, n);

return ret;