[mirror_ubuntu-jammy-kernel.git] / arch / x86 / kernel / hw_breakpoint.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *
 * Copyright (C) 2007 Alan Stern
 * Copyright (C) 2009 IBM Corporation
 * Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
 *
 * Authors: Alan Stern <stern@rowland.harvard.edu>
 *          K.Prasad <prasad@linux.vnet.ibm.com>
 *          Frederic Weisbecker <fweisbec@gmail.com>
 */

/*
 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
 * using the CPU's debug registers.
 */

#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#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/export.h>
#include <linux/sched.h>
#include <linux/smp.h>

#include <asm/hw_breakpoint.h>
#include <asm/processor.h>
#include <asm/debugreg.h>
#include <asm/user.h>
#include <asm/desc.h>
#include <asm/tlbflush.h>

/* Per cpu debug control register value */
DEFINE_PER_CPU(unsigned long, cpu_dr7);
EXPORT_PER_CPU_SYMBOL(cpu_dr7);

/* Per cpu debug address registers values */
static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);

/*
 * Stores the breakpoints currently in use on each breakpoint address
 * register for each cpus
 */
static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);


static inline unsigned long
__encode_dr7(int drnum, unsigned int len, unsigned int type)
{
        unsigned long bp_info;

        bp_info = (len | type) & 0xf;
        bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
        bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));

        return bp_info;
}

/*
 * Encode the length, type, Exact, and Enable bits for a particular breakpoint
 * as stored in debug register 7.
 */
unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
{
        return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
}

/*
 * Decode the length and type bits for a particular breakpoint as
 * stored in debug register 7.  Return the "enabled" status.
 */
int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
{
        int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);

        *len = (bp_info & 0xc) | 0x40;
        *type = (bp_info & 0x3) | 0x80;

        return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
}

/*
 * Install a perf counter breakpoint.
 *
 * We seek a free debug address register and use it for this
 * breakpoint. Eventually we enable it in the debug control register.
 *
 * Atomic: we hold the counter->ctx->lock and we only handle variables
 * and registers local to this cpu.
 */
int arch_install_hw_breakpoint(struct perf_event *bp)
{
        struct arch_hw_breakpoint *info = counter_arch_bp(bp);
        unsigned long *dr7;
        int i;

        lockdep_assert_irqs_disabled();

        for (i = 0; i < HBP_NUM; i++) {
                struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);

                if (!*slot) {
                        *slot = bp;
                        break;
                }
        }

        if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
                return -EBUSY;

        set_debugreg(info->address, i);
        __this_cpu_write(cpu_debugreg[i], info->address);

        dr7 = this_cpu_ptr(&cpu_dr7);
        *dr7 |= encode_dr7(i, info->len, info->type);

        /*
         * Ensure we first write cpu_dr7 before we set the DR7 register.
         * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
         */
        barrier();

        set_debugreg(*dr7, 7);
        if (info->mask)
                set_dr_addr_mask(info->mask, i);

        return 0;
}

/*
 * Uninstall the breakpoint contained in the given counter.
 *
 * First we search the debug address register it uses and then we disable
 * it.
 *
 * Atomic: we hold the counter->ctx->lock and we only handle variables
 * and registers local to this cpu.
 */
void arch_uninstall_hw_breakpoint(struct perf_event *bp)
{
        struct arch_hw_breakpoint *info = counter_arch_bp(bp);
        unsigned long dr7;
        int i;

        lockdep_assert_irqs_disabled();

        for (i = 0; i < HBP_NUM; i++) {
                struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);

                if (*slot == bp) {
                        *slot = NULL;
                        break;
                }
        }

        if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
                return;

        dr7 = this_cpu_read(cpu_dr7);
        dr7 &= ~__encode_dr7(i, info->len, info->type);

        set_debugreg(dr7, 7);
        if (info->mask)
                set_dr_addr_mask(0, i);

        /*
         * Ensure the write to cpu_dr7 is after we've set the DR7 register.
         * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
         */
        barrier();

        this_cpu_write(cpu_dr7, dr7);
}

static int arch_bp_generic_len(int x86_len)
{
        switch (x86_len) {
        case X86_BREAKPOINT_LEN_1:
                return HW_BREAKPOINT_LEN_1;
        case X86_BREAKPOINT_LEN_2:
                return HW_BREAKPOINT_LEN_2;
        case X86_BREAKPOINT_LEN_4:
                return HW_BREAKPOINT_LEN_4;
#ifdef CONFIG_X86_64
        case X86_BREAKPOINT_LEN_8:
                return HW_BREAKPOINT_LEN_8;
#endif
        default:
                return -EINVAL;
        }
}

int arch_bp_generic_fields(int x86_len, int x86_type,
                           int *gen_len, int *gen_type)
{
        int len;

        /* Type */
        switch (x86_type) {
        case X86_BREAKPOINT_EXECUTE:
                if (x86_len != X86_BREAKPOINT_LEN_X)
                        return -EINVAL;

                *gen_type = HW_BREAKPOINT_X;
                *gen_len = sizeof(long);
                return 0;
        case X86_BREAKPOINT_WRITE:
                *gen_type = HW_BREAKPOINT_W;
                break;
        case X86_BREAKPOINT_RW:
                *gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
                break;
        default:
                return -EINVAL;
        }

        /* Len */
        len = arch_bp_generic_len(x86_len);
        if (len < 0)
                return -EINVAL;
        *gen_len = len;

        return 0;
}

/*
 * Check for virtual address in kernel space.
 */
int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw)
{
        unsigned long va;
        int len;

        va = hw->address;
        len = arch_bp_generic_len(hw->len);
        WARN_ON_ONCE(len < 0);

        /*
         * We don't need to worry about va + len - 1 overflowing:
         * we already require that va is aligned to a multiple of len.
         */
        return (va >= TASK_SIZE_MAX) || ((va + len - 1) >= TASK_SIZE_MAX);
}

/*
 * Checks whether the range [addr, end], overlaps the area [base, base + size).
 */
static inline bool within_area(unsigned long addr, unsigned long end,
                               unsigned long base, unsigned long size)
{
        return end >= base && addr < (base + size);
}

/*
 * Checks whether the range from addr to end, inclusive, overlaps the fixed
 * mapped CPU entry area range or other ranges used for CPU entry.
 */
static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
{
        int cpu;

        /* CPU entry erea is always used for CPU entry */
        if (within_area(addr, end, CPU_ENTRY_AREA_BASE,
                        CPU_ENTRY_AREA_TOTAL_SIZE))
                return true;

        /*
         * When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
         * GSBASE value via __per_cpu_offset or pcpu_unit_offsets.
         */
#ifdef CONFIG_SMP
        if (within_area(addr, end, (unsigned long)__per_cpu_offset,
                        sizeof(unsigned long) * nr_cpu_ids))
                return true;
#else
        if (within_area(addr, end, (unsigned long)&pcpu_unit_offsets,
                        sizeof(pcpu_unit_offsets)))
                return true;
#endif

        for_each_possible_cpu(cpu) {
                /* The original rw GDT is being used after load_direct_gdt() */
                if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),
                                GDT_SIZE))
                        return true;

                /*
                 * cpu_tss_rw is not directly referenced by hardware, but
                 * cpu_tss_rw is also used in CPU entry code,
                 */
                if (within_area(addr, end,
                                (unsigned long)&per_cpu(cpu_tss_rw, cpu),
                                sizeof(struct tss_struct)))
                        return true;

                /*
                 * cpu_tlbstate.user_pcid_flush_mask is used for CPU entry.
                 * If a data breakpoint on it, it will cause an unwanted #DB.
                 * Protect the full cpu_tlbstate structure to be sure.
                 */
                if (within_area(addr, end,
                                (unsigned long)&per_cpu(cpu_tlbstate, cpu),
                                sizeof(struct tlb_state)))
                        return true;
        }

        return false;
}

static int arch_build_bp_info(struct perf_event *bp,
                              const struct perf_event_attr *attr,
                              struct arch_hw_breakpoint *hw)
{
        unsigned long bp_end;

        bp_end = attr->bp_addr + attr->bp_len - 1;
        if (bp_end < attr->bp_addr)
                return -EINVAL;

        /*
         * Prevent any breakpoint of any type that overlaps the CPU
         * entry area and data.  This protects the IST stacks and also
         * reduces the chance that we ever find out what happens if
         * there's a data breakpoint on the GDT, IDT, or TSS.
         */
        if (within_cpu_entry(attr->bp_addr, bp_end))
                return -EINVAL;

        hw->address = attr->bp_addr;
        hw->mask = 0;

        /* Type */
        switch (attr->bp_type) {
        case HW_BREAKPOINT_W:
                hw->type = X86_BREAKPOINT_WRITE;
                break;
        case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
                hw->type = X86_BREAKPOINT_RW;
                break;
        case HW_BREAKPOINT_X:
                /*
                 * We don't allow kernel breakpoints in places that are not
                 * acceptable for kprobes.  On non-kprobes kernels, we don't
                 * allow kernel breakpoints at all.
                 */
                if (attr->bp_addr >= TASK_SIZE_MAX) {
                        if (within_kprobe_blacklist(attr->bp_addr))
                                return -EINVAL;
                }

                hw->type = X86_BREAKPOINT_EXECUTE;
                /*
                 * x86 inst breakpoints need to have a specific undefined len.
                 * But we still need to check userspace is not trying to setup
                 * an unsupported length, to get a range breakpoint for example.
                 */
                if (attr->bp_len == sizeof(long)) {
                        hw->len = X86_BREAKPOINT_LEN_X;
                        return 0;
                }
                fallthrough;
        default:
                return -EINVAL;
        }

        /* Len */
        switch (attr->bp_len) {
        case HW_BREAKPOINT_LEN_1:
                hw->len = X86_BREAKPOINT_LEN_1;
                break;
        case HW_BREAKPOINT_LEN_2:
                hw->len = X86_BREAKPOINT_LEN_2;
                break;
        case HW_BREAKPOINT_LEN_4:
                hw->len = X86_BREAKPOINT_LEN_4;
                break;
#ifdef CONFIG_X86_64
        case HW_BREAKPOINT_LEN_8:
                hw->len = X86_BREAKPOINT_LEN_8;
                break;
#endif
        default:
                /* AMD range breakpoint */
                if (!is_power_of_2(attr->bp_len))
                        return -EINVAL;
                if (attr->bp_addr & (attr->bp_len - 1))
                        return -EINVAL;

                if (!boot_cpu_has(X86_FEATURE_BPEXT))
                        return -EOPNOTSUPP;

                /*
                 * It's impossible to use a range breakpoint to fake out
                 * user vs kernel detection because bp_len - 1 can't
                 * have the high bit set.  If we ever allow range instruction
                 * breakpoints, then we'll have to check for kprobe-blacklisted
                 * addresses anywhere in the range.
                 */
                hw->mask = attr->bp_len - 1;
                hw->len = X86_BREAKPOINT_LEN_1;
        }

        return 0;
}

/*
 * Validate the arch-specific HW Breakpoint register settings
 */
int hw_breakpoint_arch_parse(struct perf_event *bp,
                             const struct perf_event_attr *attr,
                             struct arch_hw_breakpoint *hw)
{
        unsigned int align;
        int ret;


        ret = arch_build_bp_info(bp, attr, hw);
        if (ret)
                return ret;

        switch (hw->len) {
        case X86_BREAKPOINT_LEN_1:
                align = 0;
                if (hw->mask)
                        align = hw->mask;
                break;
        case X86_BREAKPOINT_LEN_2:
                align = 1;
                break;
        case X86_BREAKPOINT_LEN_4:
                align = 3;
                break;
#ifdef CONFIG_X86_64
        case X86_BREAKPOINT_LEN_8:
                align = 7;
                break;
#endif
        default:
                WARN_ON_ONCE(1);
                return -EINVAL;
        }

        /*
         * Check that the low-order bits of the address are appropriate
         * for the alignment implied by len.
         */
        if (hw->address & align)
                return -EINVAL;

        return 0;
}

/*
 * Release the user breakpoints used by ptrace
 */
void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
{
        int i;
        struct thread_struct *t = &tsk->thread;

        for (i = 0; i < HBP_NUM; i++) {
                unregister_hw_breakpoint(t->ptrace_bps[i]);
                t->ptrace_bps[i] = NULL;
        }

        t->virtual_dr6 = 0;
        t->ptrace_dr7 = 0;
}

void hw_breakpoint_restore(void)
{
        set_debugreg(__this_cpu_read(cpu_debugreg[0]), 0);
        set_debugreg(__this_cpu_read(cpu_debugreg[1]), 1);
        set_debugreg(__this_cpu_read(cpu_debugreg[2]), 2);
        set_debugreg(__this_cpu_read(cpu_debugreg[3]), 3);
        set_debugreg(DR6_RESERVED, 6);
        set_debugreg(__this_cpu_read(cpu_dr7), 7);
}
EXPORT_SYMBOL_GPL(hw_breakpoint_restore);

/*
 * Handle debug exception notifications.
 *
 * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
 *
 * NOTIFY_DONE returned if one of the following conditions is true.
 * i) When the causative address is from user-space and the exception
 * is a valid one, i.e. not triggered as a result of lazy debug register
 * switching
 * ii) When there are more bits than trap<n> set in DR6 register (such
 * as BD, BS or BT) indicating that more than one debug condition is
 * met and requires some more action in do_debug().
 *
 * NOTIFY_STOP returned for all other cases
 *
 */
static int hw_breakpoint_handler(struct die_args *args)
{
        int i, rc = NOTIFY_STOP;
        struct perf_event *bp;
        unsigned long *dr6_p;
        unsigned long dr6;
        bool bpx;

        /* The DR6 value is pointed by args->err */
        dr6_p = (unsigned long *)ERR_PTR(args->err);
        dr6 = *dr6_p;

        /* Do an early return if no trap bits are set in DR6 */
        if ((dr6 & DR_TRAP_BITS) == 0)
                return NOTIFY_DONE;

        /* Handle all the breakpoints that were triggered */
        for (i = 0; i < HBP_NUM; ++i) {
                if (likely(!(dr6 & (DR_TRAP0 << i))))
                        continue;

                bp = this_cpu_read(bp_per_reg[i]);
                if (!bp)
                        continue;

                bpx = bp->hw.info.type == X86_BREAKPOINT_EXECUTE;

                /*
                 * TF and data breakpoints are traps and can be merged, however
                 * instruction breakpoints are faults and will be raised
                 * separately.
                 *
                 * However DR6 can indicate both TF and instruction
                 * breakpoints. In that case take TF as that has precedence and
                 * delay the instruction breakpoint for the next exception.
                 */
                if (bpx && (dr6 & DR_STEP))
                        continue;

                /*
                 * Reset the 'i'th TRAP bit in dr6 to denote completion of
                 * exception handling
                 */
                (*dr6_p) &= ~(DR_TRAP0 << i);

                perf_bp_event(bp, args->regs);

                /*
                 * Set up resume flag to avoid breakpoint recursion when
                 * returning back to origin.
                 */
                if (bpx)
                        args->regs->flags |= X86_EFLAGS_RF;
        }

        /*
         * Further processing in do_debug() is needed for a) user-space
         * breakpoints (to generate signals) and b) when the system has
         * taken exception due to multiple causes
         */
        if ((current->thread.virtual_dr6 & DR_TRAP_BITS) ||
            (dr6 & (~DR_TRAP_BITS)))
                rc = NOTIFY_DONE;

        return rc;
}

/*
 * Handle debug exception notifications.
 */
int 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);
}

void hw_breakpoint_pmu_read(struct perf_event *bp)
{
        /* TODO */
}