Hi Stepan, > 27.04.2019 в 00:46:53 +0200 Lukasz Majewski написал: > > Hi Arnd, > > > > > 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. Yes. You are right. The tv_nsec is 32 bit. > > (I am wondering whether such trucation is undefined behaviour in C According to [1] - Chapter 6.3.1.3 - Point 3 it is implementation-defined. > and > whether there should be sign-extension instead of zeroing-out for the > in_compat_syscall() case though.) What I've found is that "typically" the high order bits are discarded. However, it is still "implementation dependent". > > > > 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@xxxxxxxxxxxxxxxxxxxxx/ > > > Cc: Lukasz Majewski <lukma@xxxxxxx> Cc: Stepan Golosunov > > > <stepan@xxxxxxxxxxxxxxx> Signed-off-by: Arnd Bergmann > > > <arnd@xxxxxxxx> --- > > > 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 Note: [1] - http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf Best regards, Lukasz Majewski -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@xxxxxxx
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