27.04.2019 в 00:46:53 +0200 Lukasz Majewski написал:

Hi Arnd,

quoted

As Stepan Golosunov points out, we made a small mistake in the
get_timespec64() function in the kernel. It was originally added under
the assumption that CONFIG_64BIT_TIME would get enabled on all 32-bit
and 64-bit architectures, but when I did the conversion, I only turned
it on for 32-bit ones.

The effect is that the get_timespec64() function never clears the
upper half of the tv_nsec field for 32-bit tasks in compat mode.
Clearing this is required for POSIX compliant behavior of functions
that pass a 'timespec' structure with a 64-bit tv_sec and a 32-bit
tv_nsec, plus uninitialized padding.

At least for my setup (32bit ARM with 64 bit time support) this patch is
not fixing anything.

The patch is not supposed to fix anything on 32-bit architectures as
in-kernel struct timespec64 has 32-bit tv_nsec there.  Thus truncation
should happen automatically.  I also missed that fact when I was
reading get_timespec64 code.

(I am wondering whether such trucation is undefined behaviour in C and
whether there should be sign-extension instead of zeroing-out for the
in_compat_syscall() case though.)

quoted

The easiest fix for linux-5.1 is to just make the Kconfig symbol
unconditional, as it was originally intended. As a follow-up,
we should remove any #ifdef CONFIG_64BIT_TIME completely.

Link:
https://lore.kernel.org/lkml/20190422090710.bmxdhhankurhafxq@sghpc.golosunov.pp.ru/ (local)
Cc: Lukasz Majewski <lukma@denx.de> Cc: Stepan Golosunov
[off-list ref] Signed-off-by: Arnd Bergmann [off-list ref]
---
Please apply this one as a bugfix for 5.1
---
 arch/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 33687dddd86a..9092e0ffe4d3 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig

@@ -764,7 +764,7 @@ config COMPAT_OLD_SIGACTION
 	bool
 
 config 64BIT_TIME
-	def_bool ARCH_HAS_64BIT_TIME
+	def_bool y
 	help
 	  This should be selected by all architectures that need to

support new system calls with a 64-bit time_t. This is relevant on
all 32-bit