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authorArnd Bergmann <arnd@arndb.de>2017-06-20 23:10:41 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-09-27 14:39:19 +0200
commitf61a07f3fe97c26ec99531be8aad6c7fae3f714d (patch)
treef2a864d3181b41e67027f51f94000484f9cc370f /include
parent2f8b06f906fd5e7b71a001c9f8766550d6992331 (diff)
tty: improve tty_insert_flip_char() fast path
commit 979990c6284814617d8f2179d197f72ff62b5d85 upstream. kernelci.org reports a crazy stack usage for the VT code when CONFIG_KASAN is enabled: drivers/tty/vt/keyboard.c: In function 'kbd_keycode': drivers/tty/vt/keyboard.c:1452:1: error: the frame size of 2240 bytes is larger than 2048 bytes [-Werror=frame-larger-than=] The problem is that tty_insert_flip_char() gets inlined many times into kbd_keycode(), and also into other functions, and each copy requires 128 bytes for stack redzone to check for a possible out-of-bounds access on the 'ch' and 'flags' arguments that are passed into tty_insert_flip_string_flags as a variable-length string. This introduces a new __tty_insert_flip_char() function for the slow path, which receives the two arguments by value. This completely avoids the problem and the stack usage goes back down to around 100 bytes. Without KASAN, this is also slightly better, as we don't have to spill the arguments to the stack but can simply pass 'ch' and 'flag' in registers, saving a few bytes in .text for each call site. This should be backported to linux-4.0 or later, which first introduced the stack sanitizer in the kernel. Fixes: c420f167db8c ("kasan: enable stack instrumentation") Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/tty_flip.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h
index c28dd523f96e..d43837f2ce3a 100644
--- a/include/linux/tty_flip.h
+++ b/include/linux/tty_flip.h
@@ -12,6 +12,7 @@ extern int tty_prepare_flip_string(struct tty_port *port,
unsigned char **chars, size_t size);
extern void tty_flip_buffer_push(struct tty_port *port);
void tty_schedule_flip(struct tty_port *port);
+int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag);
static inline int tty_insert_flip_char(struct tty_port *port,
unsigned char ch, char flag)
@@ -26,7 +27,7 @@ static inline int tty_insert_flip_char(struct tty_port *port,
*char_buf_ptr(tb, tb->used++) = ch;
return 1;
}
- return tty_insert_flip_string_flags(port, &ch, &flag, 1);
+ return __tty_insert_flip_char(port, ch, flag);
}
static inline int tty_insert_flip_string(struct tty_port *port,