Re: [PATCH 1/2] y2038: make CONFIG_64BIT_TIME unconditional
From: Lukasz Majewski <lukma@denx.de>
Date: 2019-04-26 22:47:14
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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.
On my 32 bit ARM setup (with CONFIG_COMPAT_32BIT_TIME=y) for Y2038 test: - I do use clock_settime64 [1] to set 64 bit tv_sec with 32 bit tv_nsec and 32 bit unnamed padding. - I also may use clock_settime32 as a fallback (but it will not work beyond Y2038) if the 64 bit version is not available for any reason. In the get_timespec64() the in_compat_syscall() returns 0 [2], so the padding bits are not cleared. This imposes the in glibc requirement to zero the padding before passing it to the Linux kernel. At least for my setup (32bit ARM with 64 bit time support) this patch is not fixing anything. Moreover, the described above problem doesn't matter on native 64 bit systems as there both fields are 64 bit (no padding required). Note: [1] - https://elixir.bootlin.com/linux/v5.1-rc6/source/arch/arm/tools/syscall.tbl#L421 [2] - include/linux/compat.h -> CONFIG_COMPAT is not defined - as a result in_compat_syscall() returns 0.
quoted hunk ↗ jump to hunk
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 tosupport new system calls with a 64-bit time_t. This is relevant on all 32-bit
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@denx.de
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