From: Douglas Anderson dianders@chromium.org
[ Upstream commit 22c9e58299e5f18274788ce54c03d4fb761e3c5d ]
This is commit fdfeff0f9e3d ("arm64: hw_breakpoint: Handle inexact watchpoint addresses") but ported to arm32, which has the same problem.
This problem was found by Android CTS tests, notably the "watchpoint_imprecise" test [1]. I tested locally against a copycat (simplified) version of the test though.
[1] https://android.googlesource.com/platform/bionic/+/master/tests/sys_ptrace_t...
Link: https://lkml.kernel.org/r/20191019111216.1.I82eae759ca6dc28a245b043f485ca490...
Signed-off-by: Douglas Anderson dianders@chromium.org Reviewed-by: Matthias Kaehlcke mka@chromium.org Acked-by: Will Deacon will@kernel.org Signed-off-by: Russell King rmk+kernel@armlinux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm/kernel/hw_breakpoint.c | 100 +++++++++++++++++++++++--------- 1 file changed, 72 insertions(+), 28 deletions(-)
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c index 5f95e4b911a0b..7021ef0b4e71b 100644 --- a/arch/arm/kernel/hw_breakpoint.c +++ b/arch/arm/kernel/hw_breakpoint.c @@ -680,6 +680,40 @@ static void disable_single_step(struct perf_event *bp) arch_install_hw_breakpoint(bp); }
+/* + * Arm32 hardware does not always report a watchpoint hit address that matches + * one of the watchpoints set. It can also report an address "near" the + * watchpoint if a single instruction access both watched and unwatched + * addresses. There is no straight-forward way, short of disassembling the + * offending instruction, to map that address back to the watchpoint. This + * function computes the distance of the memory access from the watchpoint as a + * heuristic for the likelyhood that a given access triggered the watchpoint. + * + * See this same function in the arm64 platform code, which has the same + * problem. + * + * The function returns the distance of the address from the bytes watched by + * the watchpoint. In case of an exact match, it returns 0. + */ +static u32 get_distance_from_watchpoint(unsigned long addr, u32 val, + struct arch_hw_breakpoint_ctrl *ctrl) +{ + u32 wp_low, wp_high; + u32 lens, lene; + + lens = __ffs(ctrl->len); + lene = __fls(ctrl->len); + + wp_low = val + lens; + wp_high = val + lene; + if (addr < wp_low) + return wp_low - addr; + else if (addr > wp_high) + return addr - wp_high; + else + return 0; +} + static int watchpoint_fault_on_uaccess(struct pt_regs *regs, struct arch_hw_breakpoint *info) { @@ -689,23 +723,25 @@ static int watchpoint_fault_on_uaccess(struct pt_regs *regs, static void watchpoint_handler(unsigned long addr, unsigned int fsr, struct pt_regs *regs) { - int i, access; - u32 val, ctrl_reg, alignment_mask; + int i, access, closest_match = 0; + u32 min_dist = -1, dist; + u32 val, ctrl_reg; struct perf_event *wp, **slots; struct arch_hw_breakpoint *info; struct arch_hw_breakpoint_ctrl ctrl;
slots = this_cpu_ptr(wp_on_reg);
+ /* + * Find all watchpoints that match the reported address. If no exact + * match is found. Attribute the hit to the closest watchpoint. + */ + rcu_read_lock(); for (i = 0; i < core_num_wrps; ++i) { - rcu_read_lock(); - wp = slots[i]; - if (wp == NULL) - goto unlock; + continue;
- info = counter_arch_bp(wp); /* * The DFAR is an unknown value on debug architectures prior * to 7.1. Since we only allow a single watchpoint on these @@ -714,33 +750,31 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr, */ if (debug_arch < ARM_DEBUG_ARCH_V7_1) { BUG_ON(i > 0); + info = counter_arch_bp(wp); info->trigger = wp->attr.bp_addr; } else { - if (info->ctrl.len == ARM_BREAKPOINT_LEN_8) - alignment_mask = 0x7; - else - alignment_mask = 0x3; - - /* Check if the watchpoint value matches. */ - val = read_wb_reg(ARM_BASE_WVR + i); - if (val != (addr & ~alignment_mask)) - goto unlock; - - /* Possible match, check the byte address select. */ - ctrl_reg = read_wb_reg(ARM_BASE_WCR + i); - decode_ctrl_reg(ctrl_reg, &ctrl); - if (!((1 << (addr & alignment_mask)) & ctrl.len)) - goto unlock; - /* Check that the access type matches. */ if (debug_exception_updates_fsr()) { access = (fsr & ARM_FSR_ACCESS_MASK) ? HW_BREAKPOINT_W : HW_BREAKPOINT_R; if (!(access & hw_breakpoint_type(wp))) - goto unlock; + continue; }
+ val = read_wb_reg(ARM_BASE_WVR + i); + ctrl_reg = read_wb_reg(ARM_BASE_WCR + i); + decode_ctrl_reg(ctrl_reg, &ctrl); + dist = get_distance_from_watchpoint(addr, val, &ctrl); + if (dist < min_dist) { + min_dist = dist; + closest_match = i; + } + /* Is this an exact match? */ + if (dist != 0) + continue; + /* We have a winner. */ + info = counter_arch_bp(wp); info->trigger = addr; }
@@ -762,13 +796,23 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr, * we can single-step over the watchpoint trigger. */ if (!is_default_overflow_handler(wp)) - goto unlock; - + continue; step: enable_single_step(wp, instruction_pointer(regs)); -unlock: - rcu_read_unlock(); } + + if (min_dist > 0 && min_dist != -1) { + /* No exact match found. */ + wp = slots[closest_match]; + info = counter_arch_bp(wp); + info->trigger = addr; + pr_debug("watchpoint fired: address = 0x%x\n", info->trigger); + perf_bp_event(wp, regs); + if (is_default_overflow_handler(wp)) + enable_single_step(wp, instruction_pointer(regs)); + } + + rcu_read_unlock(); }
static void watchpoint_single_step_handler(unsigned long pc)