From 6eebdda35e6b18d0dddb2a44e34211bd94f0cad6 Mon Sep 17 00:00:00 2001 From: Ian Campbell Date: Fri, 24 Aug 2012 23:58:47 +0400 Subject: x86: Drop unnecessary kernel_eflags variable on 64-bit On 64 bit x86 we save the current eflags in cpu_init for use in ret_from_fork. Strictly speaking reserved bits in EFLAGS should be read as written but in practise it is unlikely that EFLAGS could ever be extended in this way and the kernel alread clears any undefined flags early on. The equivalent 32 bit code simply hard codes 0x0202 as the new EFLAGS. This change makes 64 bit use the same mechanism to setup the initial EFLAGS on fork. Note that 64 bit resets EFLAGS before calling schedule_tail() as opposed to 32 bit which calls schedule_tail() first. Therefore the correct value for EFLAGS has opposite IF bit. Signed-off-by: Ian Campbell Signed-off-by: Cyrill Gorcunov Acked-by: Andi Kleen Acked-by: "H. Peter Anvin" Cc: Brian Gerst Cc: Peter Zijlstra Cc: Pekka Enberg Cc: Andi Kleen Link: http://lkml.kernel.org/r/20120824195847.GA31628@moon Signed-off-by: Ingo Molnar --- arch/x86/include/asm/processor.h | 1 - 1 file changed, 1 deletion(-) (limited to 'arch/x86/include/asm/processor.h') diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index d048cad9bca..9738b39e4eb 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -423,7 +423,6 @@ DECLARE_INIT_PER_CPU(irq_stack_union); DECLARE_PER_CPU(char *, irq_stack_ptr); DECLARE_PER_CPU(unsigned int, irq_count); -extern unsigned long kernel_eflags; extern asmlinkage void ignore_sysret(void); #else /* X86_64 */ #ifdef CONFIG_CC_STACKPROTECTOR -- cgit v1.2.3-70-g09d2 From 9bd1190a11c9d2c59d35cb999b8d170ad52aab5f Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 3 Sep 2012 15:24:17 +0200 Subject: uprobes/x86: Do not (ab)use TIF_SINGLESTEP/user_*_single_step() for single-stepping user_enable/disable_single_step() was designed for ptrace, it assumes a single user and does unnecessary and wrong things for uprobes. For example: - arch_uprobe_enable_step() can't trust TIF_SINGLESTEP, an application itself can set X86_EFLAGS_TF which must be preserved after arch_uprobe_disable_step(). - we do not want to set TIF_SINGLESTEP/TIF_FORCED_TF in arch_uprobe_enable_step(), this only makes sense for ptrace. - otoh we leak TIF_SINGLESTEP if arch_uprobe_disable_step() doesn't do user_disable_single_step(), the application will be killed after the next syscall. - arch_uprobe_enable_step() does access_process_vm() we do not need/want. Change arch_uprobe_enable/disable_step() to set/clear X86_EFLAGS_TF directly, this is much simpler and more correct. However, we need to clear TIF_BLOCKSTEP/DEBUGCTLMSR_BTF before executing the probed insn, add set_task_blockstep(false). Note: with or without this patch, there is another (hopefully minor) problem. A probed "pushf" insn can see the wrong X86_EFLAGS_TF set by uprobes. Perhaps we should change _disable to update the stack, or teach arch_uprobe_skip_sstep() to emulate this insn. Signed-off-by: Oleg Nesterov Acked-by: Srikar Dronamraju --- arch/x86/include/asm/processor.h | 2 ++ arch/x86/kernel/step.c | 2 +- arch/x86/kernel/uprobes.c | 32 ++++++++++++++++++-------------- 3 files changed, 21 insertions(+), 15 deletions(-) (limited to 'arch/x86/include/asm/processor.h') diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index d048cad9bca..433d2e5c98a 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -759,6 +759,8 @@ static inline void update_debugctlmsr(unsigned long debugctlmsr) wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr); } +extern void set_task_blockstep(struct task_struct *task, bool on); + /* * from system description table in BIOS. Mostly for MCA use, but * others may find it useful: diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index f89cdc6ccd5..cd3b2438a98 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -157,7 +157,7 @@ static int enable_single_step(struct task_struct *child) return 1; } -static void set_task_blockstep(struct task_struct *task, bool on) +void set_task_blockstep(struct task_struct *task, bool on) { unsigned long debugctl; diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 309a0e02b12..3b4aae68efe 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -683,26 +683,30 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs) void arch_uprobe_enable_step(struct arch_uprobe *auprobe) { - struct uprobe_task *utask = current->utask; - struct arch_uprobe_task *autask = &utask->autask; + struct task_struct *task = current; + struct arch_uprobe_task *autask = &task->utask->autask; + struct pt_regs *regs = task_pt_regs(task); autask->restore_flags = 0; - if (!test_tsk_thread_flag(current, TIF_SINGLESTEP) && - !(auprobe->fixups & UPROBE_FIX_SETF)) + if (!(regs->flags & X86_EFLAGS_TF) && + !(auprobe->fixups & UPROBE_FIX_SETF)) autask->restore_flags |= UPROBE_CLEAR_TF; - /* - * The state of TIF_BLOCKSTEP is not saved. With the TF flag set we - * would to examine the opcode and the flags to make it right. Without - * TF block stepping makes no sense. - */ - user_enable_single_step(current); + + regs->flags |= X86_EFLAGS_TF; + if (test_tsk_thread_flag(task, TIF_BLOCKSTEP)) + set_task_blockstep(task, false); } void arch_uprobe_disable_step(struct arch_uprobe *auprobe) { - struct uprobe_task *utask = current->utask; - struct arch_uprobe_task *autask = &utask->autask; - + struct task_struct *task = current; + struct arch_uprobe_task *autask = &task->utask->autask; + struct pt_regs *regs = task_pt_regs(task); + /* + * The state of TIF_BLOCKSTEP was not saved so we can get an extra + * SIGTRAP if we do not clear TF. We need to examine the opcode to + * make it right. + */ if (autask->restore_flags & UPROBE_CLEAR_TF) - user_disable_single_step(current); + regs->flags &= ~X86_EFLAGS_TF; } -- cgit v1.2.3-70-g09d2