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From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
	linux-mm@kvack.org, viro@zeniv.linux.org.uk,
	linus.walleij@linaro.org, arnd@arndb.de
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/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

WARNING: multiple messages have this Message-ID (diff)
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/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-10-30 16:53 UTC|newest]

Thread overview: 39+ 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 15:45 ` Arnd Bergmann
2020-10-30 15:45 ` [PATCH 3/9] ARM: oabi-compat: add epoll_pwait handler 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   ` Arnd Bergmann
2020-10-30 15:49   ` [PATCH 2/9] ARM: traps: use get_kernel_nofault instead of set_fs() Arnd Bergmann
2020-10-30 15:49     ` Arnd Bergmann
2020-11-06  9:02     ` Linus Walleij
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     ` Arnd Bergmann
2020-10-30 15:49   ` [PATCH 4/9] ARM: syscall: always store thread_info->syscall Arnd Bergmann
2020-10-30 15:49     ` Arnd Bergmann
2020-10-30 16:53     ` Russell King - ARM Linux admin [this message]
2020-10-30 16:53       ` Russell King - ARM Linux admin
2020-10-30 21:28       ` Arnd Bergmann
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     ` Arnd Bergmann
2020-10-30 15:49   ` [PATCH 6/9] ARM: oabi-compat: rework sys_semtimedop emulation Arnd Bergmann
2020-10-30 15:49     ` Arnd Bergmann
2020-10-30 15:49   ` [PATCH 7/9] ARM: oabi-compat: rework fcntl64() emulation Arnd Bergmann
2020-10-30 15:49     ` Arnd Bergmann
2020-10-30 15:49   ` [PATCH 8/9] ARM: uaccess: add __{get,put}_kernel_nofault Arnd Bergmann
2020-10-30 15:49     ` Arnd Bergmann
2020-10-30 15:49   ` [PATCH 9/9] ARM: uaccess: remove set_fs() implementation Arnd Bergmann
2020-10-30 15:49     ` Arnd Bergmann
2020-11-06  8:57   ` [PATCH 1/9] mm/maccess: fix unaligned copy_{from,to}_kernel_nofault Linus Walleij
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
2020-11-06  9:36   ` 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
2020-09-07 15:36   ` Arnd Bergmann
2020-09-28  9:41   ` Linus Walleij
2020-09-28  9:41     ` Linus Walleij
2020-09-28 12:42     ` Arnd Bergmann
2020-09-28 12:42       ` Arnd Bergmann
2020-09-28 15:08       ` Russell King - ARM Linux admin
2020-09-28 15:08         ` Russell King - ARM Linux admin

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