From 5b905d77987de065bdd3a2906816b5f143df087b Mon Sep 17 00:00:00 2001 From: Ravi Bangoria Date: Wed, 2 Sep 2020 09:59:42 +0530 Subject: powerpc/watchpoint: Fix exception handling for CONFIG_HAVE_HW_BREAKPOINT=N On powerpc, ptrace watchpoint works in one-shot mode. i.e. kernel disables event every time it fires and user has to re-enable it. Also, in case of ptrace watchpoint, kernel notifies ptrace user before executing instruction. With CONFIG_HAVE_HW_BREAKPOINT=N, kernel is missing to disable ptrace event and thus it's causing infinite loop of exceptions. This is especially harmful when user watches on a data which is also read/written by kernel, eg syscall parameters. In such case, infinite exceptions happens in kernel mode which causes soft-lockup. Fixes: 9422de3e953d ("powerpc: Hardware breakpoints rewrite to handle non DABR breakpoint registers") Reported-by: Pedro Miraglia Franco de Carvalho Signed-off-by: Ravi Bangoria Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200902042945.129369-6-ravi.bangoria@linux.ibm.com --- arch/powerpc/include/asm/hw_breakpoint.h | 3 ++ arch/powerpc/kernel/process.c | 48 +++++++++++++++++++++++++++++++ arch/powerpc/kernel/ptrace/ptrace-noadv.c | 4 ++- 3 files changed, 54 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h index 81872c420476..abebfbee5b1c 100644 --- a/arch/powerpc/include/asm/hw_breakpoint.h +++ b/arch/powerpc/include/asm/hw_breakpoint.h @@ -18,6 +18,7 @@ struct arch_hw_breakpoint { u16 type; u16 len; /* length of the target data symbol */ u16 hw_len; /* length programmed in hw */ + u8 flags; }; /* Note: Don't change the first 6 bits below as they are in the same order @@ -37,6 +38,8 @@ struct arch_hw_breakpoint { #define HW_BRK_TYPE_PRIV_ALL (HW_BRK_TYPE_USER | HW_BRK_TYPE_KERNEL | \ HW_BRK_TYPE_HYP) +#define HW_BRK_FLAG_DISABLED 0x1 + /* Minimum granularity */ #ifdef CONFIG_PPC_8xx #define HW_BREAKPOINT_SIZE 0x4 diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 142680e885ad..483e36a42617 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -642,6 +642,44 @@ void do_send_trap(struct pt_regs *regs, unsigned long address, (void __user *)address); } #else /* !CONFIG_PPC_ADV_DEBUG_REGS */ + +static void do_break_handler(struct pt_regs *regs) +{ + struct arch_hw_breakpoint null_brk = {0}; + struct arch_hw_breakpoint *info; + struct ppc_inst instr = ppc_inst(0); + int type = 0; + int size = 0; + unsigned long ea; + int i; + + /* + * If underneath hw supports only one watchpoint, we know it + * caused exception. 8xx also falls into this category. + */ + if (nr_wp_slots() == 1) { + __set_breakpoint(0, &null_brk); + current->thread.hw_brk[0] = null_brk; + current->thread.hw_brk[0].flags |= HW_BRK_FLAG_DISABLED; + return; + } + + /* Otherwise findout which DAWR caused exception and disable it. */ + wp_get_instr_detail(regs, &instr, &type, &size, &ea); + + for (i = 0; i < nr_wp_slots(); i++) { + info = ¤t->thread.hw_brk[i]; + if (!info->address) + continue; + + if (wp_check_constraints(regs, instr, ea, type, size, info)) { + __set_breakpoint(i, &null_brk); + current->thread.hw_brk[i] = null_brk; + current->thread.hw_brk[i].flags |= HW_BRK_FLAG_DISABLED; + } + } +} + void do_break (struct pt_regs *regs, unsigned long address, unsigned long error_code) { @@ -653,6 +691,16 @@ void do_break (struct pt_regs *regs, unsigned long address, if (debugger_break_match(regs)) return; + /* + * We reach here only when watchpoint exception is generated by ptrace + * event (or hw is buggy!). Now if CONFIG_HAVE_HW_BREAKPOINT is set, + * watchpoint is already handled by hw_breakpoint_handler() so we don't + * have to do anything. But when CONFIG_HAVE_HW_BREAKPOINT is not set, + * we need to manually handle the watchpoint here. + */ + if (!IS_ENABLED(CONFIG_HAVE_HW_BREAKPOINT)) + do_break_handler(regs); + /* Deliver the signal to userspace */ force_sig_fault(SIGTRAP, TRAP_HWBKPT, (void __user *)address); } diff --git a/arch/powerpc/kernel/ptrace/ptrace-noadv.c b/arch/powerpc/kernel/ptrace/ptrace-noadv.c index 57a0ab822334..c9122ed91340 100644 --- a/arch/powerpc/kernel/ptrace/ptrace-noadv.c +++ b/arch/powerpc/kernel/ptrace/ptrace-noadv.c @@ -286,11 +286,13 @@ long ppc_del_hwdebug(struct task_struct *child, long data) } return ret; #else /* CONFIG_HAVE_HW_BREAKPOINT */ - if (child->thread.hw_brk[data - 1].address == 0) + if (!(child->thread.hw_brk[data - 1].flags & HW_BRK_FLAG_DISABLED) && + child->thread.hw_brk[data - 1].address == 0) return -ENOENT; child->thread.hw_brk[data - 1].address = 0; child->thread.hw_brk[data - 1].type = 0; + child->thread.hw_brk[data - 1].flags = 0; #endif /* CONFIG_HAVE_HW_BREAKPOINT */ return 0; -- cgit v1.2.3-59-g8ed1b