On Sun, 5 May 2019 18:10:54 +0400 Stepan Golosunov <[email protected]> wrote:
> 02.05.2019 в 15:04:18 +0000 Joseph Myers написал: > > On Tue, 30 Apr 2019, Lukasz Majewski wrote: > > > > > - The need for explicit clearing padding when calling syscalls > > > (as to be better safe than sorry in the future - there was related > > > discussion started by Stepan). > > > > This really isn't a difficult question. What it comes down to is > > whether the Linux kernel, in the first release version with these > > syscalls (we don't care about old -rc versions; what matters is the > > actual 5.1 release), ignores the padding. > > > > If 5.1 *release* ignores the padding, that is part of the > > kernel/userspace ABI, in accordance with the kernel principle of > > not breaking userspace. Thus, it is something userspace can rely > > on, now and in the future. > > > > If 5.1 release does not ignore the padding, syscall presence does > > not mean the padding is ignored by the kernel and so glibc needs to > > clear padding. Of course, it needs to clear padding in a *copy* of > > the value provided by the user unless the glibc API in question > > requires the timespec value in question to be in writable memory. > > > > So, which is (or will be) the case in 5.1 release? Padding ignored > > or not? If more complicated (ignored for some architectures / ABIs > > but not for others, or depending on whether compat syscalls are in > > use), then say so - give a precise description of the exact > > circumstances under which the padding around a 32-bit tv_nsec will > > or will not be ignored by the kernel on input from userspace. > > In current linux git it looks like padding is correctly ignored in > 32-bit kernels (because kernel itself has 32-bit tv_nsec there) but > the code to clear it on compat syscalls in 64-bit kernels seems to be > broken. > > The patch to fix this is at > > https://lore.kernel.org/lkml/[email protected]/ > > but it doesn't seem like it has reached Linus yet. > I hope that this patch will be pulled soon (before final cut) - for that reason we can assume that the padding is ignored by the kernel and hence do not explicitly clear it in glibc (as it was done in sent patches) > > (Hmm. I think that old ipc and socketcall syscalls in 32-bit kernels > are broken without that patch too. They would try to read > __kernel_timespec when callers are passing old_timespec32.) Please correct me if I'm wrong, but this problem is related to x32 machines (and not to ARM 32 bit ones with Y2038). 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: [email protected]
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