Re: [PATCH v3 4/6] LoongArch: Add uprobes support

[Huacai Chen]

Hi, Tiezhu,

On Wed, Apr 19, 2023 at 5:57 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
>
> Uprobes is the user-space counterpart to kprobes, this commit
> adds uprobes support for LoongArch.
>
> Here is a simple example with CONFIG_UPROBE_EVENTS=y:
>
>   # cat test.c
>   #include <stdio.h>
>
>   int add(int a, int b)
>   {
>           return a + b;
>   }
>
>   int main()
>   {
>           return add(2, 7);
>   }
>   # gcc test.c -o /tmp/test
>   # nm /tmp/test | grep add
>   0000000120004194 T add
>   # cd /sys/kernel/debug/tracing
>   # echo > uprobe_events
>   # echo "p:myuprobe /tmp/test:0x4194 %r4 %r5" > uprobe_events
>   # echo "r:myuretprobe /tmp/test:0x4194 %r4" >> uprobe_events
>   # echo 1 > events/uprobes/enable
>   # echo 1 > tracing_on
>   # /tmp/test
>   # cat trace
>   ...
>   #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
>   #              | |         |   |||||     |         |
>               test-1060    [001] DNZff  1015.770620: myuprobe: (0x120004194) arg1=0x2 arg2=0x7
>               test-1060    [001] DNZff  1015.770930: myuretprobe: (0x1200041f0 <- 0x120004194) arg1=0x9
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> ---
>  arch/loongarch/Kconfig               |   3 +
>  arch/loongarch/include/asm/uprobes.h |  36 +++++++++
>  arch/loongarch/kernel/Makefile       |   1 +
>  arch/loongarch/kernel/traps.c        |   9 +--
>  arch/loongarch/kernel/uprobes.c      | 142 +++++++++++++++++++++++++++++++++++
>  5 files changed, 186 insertions(+), 5 deletions(-)
>  create mode 100644 arch/loongarch/include/asm/uprobes.h
>  create mode 100644 arch/loongarch/kernel/uprobes.c
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 7fd5125..ab66ad2 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -574,6 +574,9 @@ config ARCH_MMAP_RND_BITS_MIN
>  config ARCH_MMAP_RND_BITS_MAX
>         default 18
>
> +config ARCH_SUPPORTS_UPROBES
> +       def_bool y
> +
>  menu "Power management options"
>
>  config ARCH_SUSPEND_POSSIBLE
> diff --git a/arch/loongarch/include/asm/uprobes.h b/arch/loongarch/include/asm/uprobes.h
> new file mode 100644
> index 0000000..59e2683
> --- /dev/null
> +++ b/arch/loongarch/include/asm/uprobes.h
> @@ -0,0 +1,36 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef __ASM_LOONGARCH_UPROBES_H
> +#define __ASM_LOONGARCH_UPROBES_H
> +
> +#include <asm/inst.h>
> +
> +typedef u32 uprobe_opcode_t;
> +
> +#define MAX_UINSN_BYTES                8
> +#define UPROBE_XOL_SLOT_BYTES  MAX_UINSN_BYTES
In old versions we define UPROBE_XOL_SLOT_BYTES to 128, why we use 8 now?

> +
> +#define UPROBE_XOLBP_INSN      larch_insn_gen_break(BRK_UPROBE_XOLBP)
> +#define UPROBE_SWBP_INSN       larch_insn_gen_break(BRK_UPROBE_BP)
> +#define UPROBE_SWBP_INSN_SIZE  LOONGARCH_INSN_SIZE
> +
> +struct arch_uprobe {
> +       union {
> +               u32 insn[2];
> +               u32 ixol[2];
> +       };
> +       bool simulate;
> +};
> +
> +struct arch_uprobe_task {
> +       unsigned long saved_trap_nr;
> +};
> +
> +#ifdef CONFIG_UPROBES
> +bool uprobe_breakpoint_handler(struct pt_regs *regs);
> +bool uprobe_singlestep_handler(struct pt_regs *regs);
> +#else /* !CONFIG_UPROBES */
> +static inline bool uprobe_breakpoint_handler(struct pt_regs *regs) { return false; }
> +static inline bool uprobe_singlestep_handler(struct pt_regs *regs) { return false; }
> +#endif /* CONFIG_UPROBES */
> +
> +#endif /* __ASM_LOONGARCH_UPROBES_H */
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index 78d4e33..67b9c26 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -53,5 +53,6 @@ obj-$(CONFIG_PERF_EVENTS)     += perf_event.o perf_regs.o
>  obj-$(CONFIG_HAVE_HW_BREAKPOINT)       += hw_breakpoint.o
>
>  obj-$(CONFIG_KPROBES)          += kprobes.o kprobes_trampoline.o
> +obj-$(CONFIG_UPROBES)          += uprobes.o
>
>  CPPFLAGS_vmlinux.lds           := $(KBUILD_CFLAGS)
> diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index de8ebe2..cfc2e0c 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -45,6 +45,7 @@
>  #include <asm/tlb.h>
>  #include <asm/types.h>
>  #include <asm/unwind.h>
> +#include <asm/uprobes.h>
>
>  #include "access-helper.h"
>
> @@ -440,7 +441,6 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
>         if (regs->csr_prmd & CSR_PRMD_PIE)
>                 local_irq_enable();
>
> -       current->thread.trap_nr = read_csr_excode();
>         if (__get_inst(&opcode, (u32 *)era, user))
>                 goto out_sigsegv;
>
> @@ -462,18 +462,17 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
>                 else
>                         break;
>         case BRK_UPROBE_BP:
> -               if (notify_die(DIE_UPROBE, "Uprobe", regs, bcode,
> -                              current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
> +               if (uprobe_breakpoint_handler(regs))
>                         goto out;
>                 else
>                         break;
>         case BRK_UPROBE_XOLBP:
> -               if (notify_die(DIE_UPROBE_XOL, "Uprobe_XOL", regs, bcode,
> -                              current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
> +               if (uprobe_singlestep_handler(regs))
As I know, XOL means "execute out of line", is it an alias of "single step"?

Huacai
>                         goto out;
>                 else
>                         break;
>         default:
> +               current->thread.trap_nr = read_csr_excode();
>                 if (notify_die(DIE_TRAP, "Break", regs, bcode,
>                                current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
>                         goto out;
> diff --git a/arch/loongarch/kernel/uprobes.c b/arch/loongarch/kernel/uprobes.c
> new file mode 100644
> index 0000000..628c39d
> --- /dev/null
> +++ b/arch/loongarch/kernel/uprobes.c
> @@ -0,0 +1,142 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <linux/highmem.h>
> +#include <linux/ptrace.h>
> +#include <linux/uprobes.h>
> +#include <linux/sched.h>
> +#include <asm/cacheflush.h>
> +
> +#define UPROBE_TRAP_NR UINT_MAX
> +
> +int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
> +                            struct mm_struct *mm, unsigned long addr)
> +{
> +       union loongarch_instruction insn;
> +
> +       if (addr & 0x3)
> +               return -EILSEQ;
> +
> +       insn.word = auprobe->insn[0];
> +
> +       if (insns_not_supported(insn))
> +               return -EINVAL;
> +
> +       if (insns_need_simulation(insn)) {
> +               auprobe->ixol[0] = larch_insn_gen_nop();
> +               auprobe->simulate = true;
> +       } else {
> +               auprobe->ixol[0] = auprobe->insn[0];
> +               auprobe->simulate = false;
> +       }
> +
> +       auprobe->ixol[1] = UPROBE_XOLBP_INSN;
> +
> +       return 0;
> +}
> +
> +int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> +{
> +       struct uprobe_task *utask = current->utask;
> +
> +       utask->autask.saved_trap_nr = current->thread.trap_nr;
> +       current->thread.trap_nr = UPROBE_TRAP_NR;
> +       instruction_pointer_set(regs, utask->xol_vaddr);
> +
> +       return 0;
> +}
> +
> +int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> +{
> +       struct uprobe_task *utask = current->utask;
> +
> +       WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
> +       current->thread.trap_nr = utask->autask.saved_trap_nr;
> +       instruction_pointer_set(regs, utask->vaddr + LOONGARCH_INSN_SIZE);
> +
> +       return 0;
> +}
> +
> +void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> +{
> +       struct uprobe_task *utask = current->utask;
> +
> +       current->thread.trap_nr = utask->autask.saved_trap_nr;
> +       instruction_pointer_set(regs, utask->vaddr);
> +}
> +
> +bool arch_uprobe_xol_was_trapped(struct task_struct *t)
> +{
> +       if (t->thread.trap_nr != UPROBE_TRAP_NR)
> +               return true;
> +
> +       return false;
> +}
> +
> +bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
> +{
> +       union loongarch_instruction insn;
> +
> +       if (!auprobe->simulate)
> +               return false;
> +
> +       insn.word = auprobe->insn[0];
> +       arch_simulate_insn(insn, regs);
> +
> +       return true;
> +}
> +
> +unsigned long arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr,
> +                                               struct pt_regs *regs)
> +{
> +       unsigned long ra = regs->regs[1];
> +
> +       regs->regs[1] = trampoline_vaddr;
> +
> +       return ra;
> +}
> +
> +bool arch_uretprobe_is_alive(struct return_instance *ret,
> +                            enum rp_check ctx, struct pt_regs *regs)
> +{
> +       if (ctx == RP_CHECK_CHAIN_CALL)
> +               return regs->regs[3] <= ret->stack;
> +       else
> +               return regs->regs[3] < ret->stack;
> +}
> +
> +int arch_uprobe_exception_notify(struct notifier_block *self,
> +                                unsigned long val, void *data)
> +{
> +       return NOTIFY_DONE;
> +}
> +
> +bool uprobe_breakpoint_handler(struct pt_regs *regs)
> +{
> +       if (uprobe_pre_sstep_notifier(regs))
> +               return true;
> +
> +       return false;
> +}
> +
> +bool uprobe_singlestep_handler(struct pt_regs *regs)
> +{
> +       if (uprobe_post_sstep_notifier(regs))
> +               return true;
> +
> +       return false;
> +}
> +
> +unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
> +{
> +       return instruction_pointer(regs);
> +}
> +
> +void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
> +                          void *src, unsigned long len)
> +{
> +       void *kaddr = kmap_local_page(page);
> +       void *dst = kaddr + (vaddr & ~PAGE_MASK);
> +
> +       memcpy(dst, src, len);
> +       flush_icache_range((unsigned long)dst, (unsigned long)dst + len);
> +       kunmap_local(kaddr);
> +}
> --
> 2.1.0
>