Messages in this thread | | | Date | Thu, 28 May 2009 16:35:15 +1000 | From | David Gibson <> | Subject | Re: [Patch 03/12] x86 architecture implementation of Hardware Breakpoint interfaces |
| |
On Mon, May 11, 2009 at 05:23:03PM +0530, K.Prasad wrote: > This patch introduces the arch-specific implementation of > hw_breakpoint.c inside x86 specific directories. They contain > functions which help validate and serve requests for using Hardware > Breakpoint registers on x86 processors.
[snip] > Index: arch/x86/kernel/hw_breakpoint.c > =================================================================== > --- /dev/null > +++ arch/x86/kernel/hw_breakpoint.c > @@ -0,0 +1,358 @@ > +/* > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License as published by > + * the Free Software Foundation; either version 2 of the License, or > + * (at your option) any later version. > + * > + * This program is distributed in the hope that it will be useful, > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > + * GNU General Public License for more details. > + * > + * You should have received a copy of the GNU General Public License > + * along with this program; if not, write to the Free Software > + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. > + * > + * Copyright (C) 2007 Alan Stern > + * Copyright (C) 2009 IBM Corporation > + */ > + > +/* > + * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility, > + * using the CPU's debug registers. > + */ > + > +#include <linux/irqflags.h> > +#include <linux/notifier.h> > +#include <linux/kallsyms.h> > +#include <linux/kprobes.h> > +#include <linux/percpu.h> > +#include <linux/kdebug.h> > +#include <linux/kernel.h> > +#include <linux/module.h> > +#include <linux/sched.h> > +#include <linux/init.h> > +#include <linux/smp.h> > + > +#include <asm/hw_breakpoint.h> > +#include <asm/processor.h> > +#include <asm/debugreg.h> > + > +/* Unmasked kernel DR7 value */ > +static unsigned long kdr7; > + > +/* > + * Masks for the bits corresponding to registers DR0 - DR3 in DR7 register. > + * Used to clear and verify the status of bits corresponding to DR0 - DR3 > + */ > +static const unsigned long dr7_masks[HB_NUM] = { > + 0x000f0003, /* LEN0, R/W0, G0, L0 */ > + 0x00f0000c, /* LEN1, R/W1, G1, L1 */ > + 0x0f000030, /* LEN2, R/W2, G2, L2 */ > + 0xf00000c0 /* LEN3, R/W3, G3, L3 */ > +}; > + > + > +/* > + * Encode the length, type, Exact, and Enable bits for a particular breakpoint > + * as stored in debug register 7. > + */ > +static unsigned long encode_dr7(int drnum, unsigned len, unsigned type) > +{ > + unsigned long temp; > + > + temp = (len | type) & 0xf; > + temp <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE); > + temp |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE)) | > + DR_GLOBAL_SLOWDOWN; > + return temp; > +} > + > +void arch_update_kernel_hw_breakpoints(void *unused) > +{ > + struct hw_breakpoint *bp; > + int i, cpu = get_cpu(); > + > + /* Don't allow debug exceptions while we update the registers */ > + set_debugreg(0UL, 7); > + > + /* Clear all kernel-space breakpoints in kdr7 */ > + kdr7 = 0; > + for (i = hbp_kernel_pos; i < HB_NUM; i++) { > + per_cpu(this_hbp_kernel[i], cpu) = bp = hbp_kernel[i]; > + if (bp) { > + kdr7 |= encode_dr7(i, bp->info.len, bp->info.type); > + set_debugreg(hbp_kernel[i]->info.address, i); > + } > + } > + > + /* No need to set DR6. Update the debug registers with kernel-space > + * breakpoint values from kdr7 and user-space requests from the > + * current process > + */ > + set_debugreg(kdr7 | current->thread.debugreg7, 7); > + put_cpu_no_resched(); > +} > + > +/* > + * Install the thread breakpoints in their debug registers. > + */ > +void arch_install_thread_hw_breakpoint(struct task_struct *tsk) > +{ > + struct thread_struct *thread = &(tsk->thread); > + > + switch (hbp_kernel_pos) { > + case 4: > + set_debugreg(thread->debugreg[3], 3); > + case 3: > + set_debugreg(thread->debugreg[2], 2); > + case 2: > + set_debugreg(thread->debugreg[1], 1); > + case 1: > + set_debugreg(thread->debugreg[0], 0); > + default: > + break; > + } > + > + /* No need to set DR6 */ > + set_debugreg((kdr7 | thread->debugreg7), 7); > +} > + > +/* > + * Install the debug register values for just the kernel, no thread. > + */ > +void arch_uninstall_thread_hw_breakpoint() > +{ > + /* Clear the user-space portion of debugreg7 by setting only kdr7 */ > + set_debugreg(kdr7, 7); > + > +} > + > +static int get_hbp_len(u8 hbp_len) > +{ > + unsigned int len_in_bytes = 0; > + > + switch (hbp_len) { > + case HW_BREAKPOINT_LEN_1: > + len_in_bytes = 1; > + break; > + case HW_BREAKPOINT_LEN_2: > + len_in_bytes = 2; > + break; > + case HW_BREAKPOINT_LEN_4: > + len_in_bytes = 4; > + break; > +#ifdef CONFIG_X86_64 > + case HW_BREAKPOINT_LEN_8: > + len_in_bytes = 8; > + break; > +#endif
Hrm, the fact that you have to do this nasty back-conversion again makes me wonder at the wisdom of having per-arch encodings for breakpoint length.
> + } > + return len_in_bytes; > +} > + > +/* > + * Check for virtual address in user space. > + */ > +int arch_check_va_in_userspace(unsigned long va, u8 hbp_len) > +{ > + unsigned int len; > + > + len = get_hbp_len(hbp_len); > + > + return (va <= TASK_SIZE - len); > +} > + > +/* > + * Check for virtual address in kernel space. > + */ > +int arch_check_va_in_kernelspace(unsigned long va, u8 hbp_len) > +{ > + unsigned int len; > + > + len = get_hbp_len(hbp_len); > + > + return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE); > +} > + > +/* > + * Store a breakpoint's encoded address, length, and type. > + */ > +static int arch_store_info(struct hw_breakpoint *bp)
This function doesn't look very arch specific. Nor is the name very meaningful.
> +{ > + /* > + * User-space requests will always have the address field populated > + * For kernel-addresses, either the address or symbol name can be > + * specified. > + */ > + if (bp->info.name) > + bp->info.address = (unsigned long) > + kallsyms_lookup_name(bp->info.name); > + if (bp->info.address) > + return 0; > + return -EINVAL; > +} > + > +/* > + * Validate the arch-specific HW Breakpoint register settings > + */ > +int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp, > + struct task_struct *tsk) > +{ > + unsigned int align; > + int ret = -EINVAL; > + > + switch (bp->info.type) { > + /* > + * Ptrace-refactoring code > + * For now, we'll allow instruction breakpoint only for user-space > + * addresses > + */ > + case HW_BREAKPOINT_EXECUTE: > + if ((!arch_check_va_in_userspace(bp->info.address, > + bp->info.len)) && > + bp->info.len != HW_BREAKPOINT_LEN_EXECUTE) > + return ret; > + break; > + case HW_BREAKPOINT_WRITE: > + break; > + case HW_BREAKPOINT_RW: > + break; > + default: > + return ret; > + } > + > + switch (bp->info.len) { > + case HW_BREAKPOINT_LEN_1: > + align = 0; > + break; > + case HW_BREAKPOINT_LEN_2: > + align = 1; > + break; > + case HW_BREAKPOINT_LEN_4: > + align = 3; > + break; > +#ifdef CONFIG_X86_64 > + case HW_BREAKPOINT_LEN_8: > + align = 7; > + break; > +#endif > + default: > + return ret; > + } > + > + if (bp->triggered) > + ret = arch_store_info(bp); > + > + if (ret < 0) > + return ret; > + /* > + * Check that the low-order bits of the address are appropriate > + * for the alignment implied by len. > + */ > + if (bp->info.address & align) > + return -EINVAL; > + > + /* Check that the virtual address is in the proper range */ > + if (tsk) { > + if (!arch_check_va_in_userspace(bp->info.address, bp->info.len)) > + return -EFAULT; > + } else { > + if (!arch_check_va_in_kernelspace(bp->info.address, > + bp->info.len)) > + return -EFAULT; > + } > + return 0; > +} > + > +void arch_update_user_hw_breakpoint(int pos, struct task_struct *tsk) > +{ > + struct thread_struct *thread = &(tsk->thread); > + struct hw_breakpoint *bp = thread->hbp[pos]; > + > + thread->debugreg7 &= ~dr7_masks[pos]; > + if (bp) { > + thread->debugreg[pos] = bp->info.address; > + thread->debugreg7 |= encode_dr7(pos, bp->info.len, > + bp->info.type); > + } else > + thread->debugreg[pos] = 0; > +} > + > +void arch_flush_thread_hw_breakpoint(struct task_struct *tsk) > +{ > + int i; > + struct thread_struct *thread = &(tsk->thread); > + > + thread->debugreg7 = 0; > + for (i = 0; i < HB_NUM; i++) > + thread->debugreg[i] = 0; > +} > + > +/* > + * Handle debug exception notifications. > + */ > +int __kprobes hw_breakpoint_handler(struct die_args *args) > +{ > + int i, cpu, rc = NOTIFY_STOP; > + struct hw_breakpoint *bp; > + /* The DR6 value is stored in args->err */ > + unsigned long dr7, dr6 = args->err; > + > + /* Do an early return if no trap bits are set in DR6 */ > + if ((dr6 & DR_TRAP_BITS) == 0) > + return NOTIFY_DONE; > + > + /* Lazy debug register switching */ > + if (!test_tsk_thread_flag(current, TIF_DEBUG)) > + switch_to_none_hw_breakpoint();
Shouldn't you also drop out of the handler here, rather than having to again check for a false alarm below.
It's also not immediately clear to me how lazy switching buys you anything here, since it's only lazy switching off, not lazy switching on.
> + get_debugreg(dr7, 7); > + /* Disable breakpoints during exception handling */ > + set_debugreg(0UL, 7); > + /* > + * Assert that local interrupts are disabled > + * Reset the DRn bits in the virtualized register value. > + * The ptrace trigger routine will add in whatever is needed. > + */ > + current->thread.debugreg6 &= ~DR_TRAP_BITS; > + cpu = get_cpu(); > + > + /* Handle all the breakpoints that were triggered */ > + for (i = 0; i < HB_NUM; ++i) { > + if (likely(!(dr6 & (DR_TRAP0 << i)))) > + continue; > + /* > + * Find the corresponding hw_breakpoint structure and > + * invoke its triggered callback. > + */ > + if (i >= hbp_kernel_pos) > + bp = per_cpu(this_hbp_kernel[i], cpu); > + else { > + bp = current->thread.hbp[i]; > + /* False alarm due to lazy DR switching */ > + if (!bp) > + continue; > + rc = NOTIFY_DONE; > + } > + (bp->triggered)(bp, args->regs); > + } > + if (dr6 & (~DR_TRAP_BITS)) > + rc = NOTIFY_DONE; > + > + set_debugreg(dr7, 7); > + put_cpu_no_resched(); > + return rc; > +} > + > +/* > + * Handle debug exception notifications. > + */ > +int __kprobes hw_breakpoint_exceptions_notify( > + struct notifier_block *unused, unsigned long val, void *data) > +{ > + if (val != DIE_DEBUG) > + return NOTIFY_DONE; > + > + return hw_breakpoint_handler(data); > +} >
-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
| |