From: Marcin Nowakowski <marcin.nowakowski@imgtec.com> To: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <james.hogan@imgtec.com>, <linux-mips@linux-mips.org> Subject: [PATCH 2/2] MIPS: ptrace: disable watchpoints if hit in kernel mode Date: Fri, 13 Jan 2017 08:44:47 +0100 [thread overview] Message-ID: <1484293487-5770-2-git-send-email-marcin.nowakowski@imgtec.com> (raw) In-Reply-To: <1484293487-5770-1-git-send-email-marcin.nowakowski@imgtec.com> If a watchpoint is hit when in kernel mode it is possible for the system to end up in an infinite loop processing the watchpoint. This can happen if a user sets a watchpoint in the kernel addess space (which is possible in certain EVA configurations) or if a user sets a watchpoint in a user area accessed directly by the kernel (eg. a user buffer accessed via a syscall). To prevent the infinite loop ensure that the watchpoint was hit in userspace, and clear the watchpoint registers otherwise. As this change could mean that a watchpoint is not hit when it should be (when returning to the interrupted traced task on exception exit), the resume_userspace path needs to be extended to conditionally restore the watchpoint configuration. If a task switch occurs when returning to userspace, the watchpoints will be restored in a typical way in the switch_to() handler. Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com> --- arch/mips/kernel/entry.S | 9 ++++++++- arch/mips/kernel/traps.c | 2 +- 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S index ef69a64..b15a9a9 100644 --- a/arch/mips/kernel/entry.S +++ b/arch/mips/kernel/entry.S @@ -55,7 +55,14 @@ resume_userspace: LONG_L a2, TI_FLAGS($28) # current->work andi t0, a2, _TIF_WORK_MASK # (ignoring syscall_trace) bnez t0, work_pending - j restore_all +#ifdef CONFIG_HARDWARE_WATCHPOINTS + li t0, _TIF_LOAD_WATCH + and t0, a2, t0 + beqz t0, 1f + PTR_L a0, TI_TASK($28) + jal mips_install_watch_registers +#endif +1: j restore_all #ifdef CONFIG_PREEMPT resume_kernel: diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c index b86ce85..d92169e 100644 --- a/arch/mips/kernel/traps.c +++ b/arch/mips/kernel/traps.c @@ -1527,7 +1527,7 @@ asmlinkage void do_watch(struct pt_regs *regs) * their values and send SIGTRAP. Otherwise another thread * left the registers set, clear them and continue. */ - if (test_tsk_thread_flag(current, TIF_LOAD_WATCH)) { + if (user_mode(regs) && test_tsk_thread_flag(current, TIF_LOAD_WATCH)) { mips_read_watch_registers(); local_irq_enable(); force_sig_info(SIGTRAP, &info, current); -- 2.7.4
WARNING: multiple messages have this Message-ID (diff)
From: Marcin Nowakowski <marcin.nowakowski@imgtec.com> To: Ralf Baechle <ralf@linux-mips.org> Cc: James Hogan <james.hogan@imgtec.com>, linux-mips@linux-mips.org Subject: [PATCH 2/2] MIPS: ptrace: disable watchpoints if hit in kernel mode Date: Fri, 13 Jan 2017 08:44:47 +0100 [thread overview] Message-ID: <1484293487-5770-2-git-send-email-marcin.nowakowski@imgtec.com> (raw) Message-ID: <20170113074447.vV30b48BiRRysuWyKYpMgN-g4ddn4Rghj0m6DnNZlYo@z> (raw) In-Reply-To: <1484293487-5770-1-git-send-email-marcin.nowakowski@imgtec.com> If a watchpoint is hit when in kernel mode it is possible for the system to end up in an infinite loop processing the watchpoint. This can happen if a user sets a watchpoint in the kernel addess space (which is possible in certain EVA configurations) or if a user sets a watchpoint in a user area accessed directly by the kernel (eg. a user buffer accessed via a syscall). To prevent the infinite loop ensure that the watchpoint was hit in userspace, and clear the watchpoint registers otherwise. As this change could mean that a watchpoint is not hit when it should be (when returning to the interrupted traced task on exception exit), the resume_userspace path needs to be extended to conditionally restore the watchpoint configuration. If a task switch occurs when returning to userspace, the watchpoints will be restored in a typical way in the switch_to() handler. Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com> --- arch/mips/kernel/entry.S | 9 ++++++++- arch/mips/kernel/traps.c | 2 +- 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S index ef69a64..b15a9a9 100644 --- a/arch/mips/kernel/entry.S +++ b/arch/mips/kernel/entry.S @@ -55,7 +55,14 @@ resume_userspace: LONG_L a2, TI_FLAGS($28) # current->work andi t0, a2, _TIF_WORK_MASK # (ignoring syscall_trace) bnez t0, work_pending - j restore_all +#ifdef CONFIG_HARDWARE_WATCHPOINTS + li t0, _TIF_LOAD_WATCH + and t0, a2, t0 + beqz t0, 1f + PTR_L a0, TI_TASK($28) + jal mips_install_watch_registers +#endif +1: j restore_all #ifdef CONFIG_PREEMPT resume_kernel: diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c index b86ce85..d92169e 100644 --- a/arch/mips/kernel/traps.c +++ b/arch/mips/kernel/traps.c @@ -1527,7 +1527,7 @@ asmlinkage void do_watch(struct pt_regs *regs) * their values and send SIGTRAP. Otherwise another thread * left the registers set, clear them and continue. */ - if (test_tsk_thread_flag(current, TIF_LOAD_WATCH)) { + if (user_mode(regs) && test_tsk_thread_flag(current, TIF_LOAD_WATCH)) { mips_read_watch_registers(); local_irq_enable(); force_sig_info(SIGTRAP, &info, current); -- 2.7.4
next prev parent reply other threads:[~2017-01-13 7:45 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-01-13 7:44 [PATCH 1/2] MIPS: ptrace: protect watchpoint handling code from setting watchpoints Marcin Nowakowski 2017-01-13 7:44 ` Marcin Nowakowski 2017-01-13 7:44 ` Marcin Nowakowski [this message] 2017-01-13 7:44 ` [PATCH 2/2] MIPS: ptrace: disable watchpoints if hit in kernel mode Marcin Nowakowski 2017-01-13 11:42 ` James Hogan 2017-01-13 11:42 ` James Hogan 2017-01-23 9:06 ` Marcin Nowakowski 2017-01-23 9:06 ` Marcin Nowakowski 2017-01-13 11:11 ` [PATCH 1/2] MIPS: ptrace: protect watchpoint handling code from setting watchpoints James Hogan 2017-01-13 11:11 ` James Hogan 2017-01-13 11:33 ` Marcin Nowakowski 2017-01-13 11:33 ` Marcin Nowakowski
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