From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Arnd Bergmann <arnd@kernel.org>
Cc: linux-arch@vger.kernel.org, arnd@arndb.de,
linus.walleij@linaro.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, viro@zeniv.linux.org.uk,
Christoph Hellwig <hch@lst.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/9] ARM: syscall: always store thread_info->syscall
Date: Fri, 30 Oct 2020 16:53:39 +0000 [thread overview]
Message-ID: <20201030165338.GG1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <20201030154919.1246645-4-arnd@kernel.org>
On Fri, Oct 30, 2020 at 04:49:14PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> The system call number is used in a a couple of places, in particular
> ptrace, seccomp and /proc/<pid>/syscall.
>
> The last one apparently never worked reliably on ARM for tasks
> that are not currently getting traced.
>
> Storing the syscall number in the normal entry path makes it work,
> as well as allowing us to see if the current system call is for
> OABI compat mode, which is the next thing I want to hook into.
I'm not sure this patch is correct.
Tracing the existing code for OABI:
asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
{
current_thread_info()->syscall = scno;
/* Legacy ABI only. */
USER( ldr scno, [saved_pc, #-4] ) @ get SWI instruction
bic scno, scno, #0xff000000 @ mask off SWI op-code
eor scno, scno, #__NR_SYSCALL_BASE @ check OS number
tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls?
bne __sys_trace
__sys_trace:
mov r1, scno
add r0, sp, #S_OFF
bl syscall_trace_enter
So, thread_info->syscall does not include __NR_SYSCALL_BASE. The
reason for this is the code that makes use of that via syscall_get_nr().
kernel/trace/trace_syscalls.c:
syscall_nr = trace_get_syscall_nr(current, regs);
if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
return;
and NR_syscalls is the number of syscalls, which doesn't include the
__NR_SYSCALL_BASE offset.
So, I think this patch actually breaks OABI.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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next prev parent reply other threads:[~2020-10-30 16:57 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-30 15:45 [PATCH v4 0/9] ARM: remove set_fs callers and implementation Arnd Bergmann
2020-10-30 15:49 ` [PATCH 1/9] mm/maccess: fix unaligned copy_{from,to}_kernel_nofault Arnd Bergmann
2020-10-30 15:49 ` [PATCH 2/9] ARM: traps: use get_kernel_nofault instead of set_fs() Arnd Bergmann
2020-11-06 9:02 ` Linus Walleij
2020-10-30 15:49 ` [PATCH 3/9] ARM: oabi-compat: add epoll_pwait handler Arnd Bergmann
2020-10-30 15:49 ` [PATCH 4/9] ARM: syscall: always store thread_info->syscall Arnd Bergmann
2020-10-30 16:53 ` Russell King - ARM Linux admin [this message]
2020-10-30 21:28 ` Arnd Bergmann
2020-10-30 15:49 ` [PATCH 5/9] ARM: oabi-compat: rework epoll_wait/epoll_pwait emulation Arnd Bergmann
2020-10-30 15:49 ` [PATCH 6/9] ARM: oabi-compat: rework sys_semtimedop emulation Arnd Bergmann
2020-10-30 15:49 ` [PATCH 7/9] ARM: oabi-compat: rework fcntl64() emulation Arnd Bergmann
2020-10-30 15:49 ` [PATCH 8/9] ARM: uaccess: add __{get,put}_kernel_nofault Arnd Bergmann
2020-10-30 15:49 ` [PATCH 9/9] ARM: uaccess: remove set_fs() implementation Arnd Bergmann
2020-11-06 8:57 ` [PATCH 1/9] mm/maccess: fix unaligned copy_{from, to}_kernel_nofault Linus Walleij
2020-11-06 9:36 ` [PATCH v4 0/9] ARM: remove set_fs callers and implementation Linus Walleij
-- strict thread matches above, loose matches on Subject: below --
2020-09-07 15:36 [PATCH " Arnd Bergmann
2020-09-07 15:36 ` [PATCH 4/9] ARM: syscall: always store thread_info->syscall Arnd Bergmann
2020-09-28 9:41 ` Linus Walleij
2020-09-28 12:42 ` Arnd Bergmann
2020-09-28 15:08 ` Russell King - ARM Linux admin
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