Re: [PATCH v2] arch/riscv: Enable kprobes when CONFIG_MODULES=n

Masami Hiramatsu
2024-03-25T02:56:59Z

Hi Jarkko,

On Sun, 24 Mar 2024 01:29:08 +0200
Jarkko Sakkinen <jarkko@kernel.org> wrote:

> Tracing with kprobes while running a monolithic kernel is currently
> impossible due the kernel module allocator dependency.
>
> Address the issue by allowing architectures to implement module_alloc()
> and module_memfree() independent of the module subsystem. An arch tree
> can signal this by setting HAVE_KPROBES_ALLOC in its Kconfig file.
>
> Realize the feature on RISC-V by separating allocator to module_alloc.c
> and implementing module_memfree().

Even though, this involves changes in arch-independent part. So it should
be solved by generic way. Did you checked Calvin's thread?

https://lore.kernel.org/all/cover.1709676663.git.jcalvinowens@gmail.com/

I think, we'd better to introduce `alloc_execmem()`,
CONFIG_HAVE_ALLOC_EXECMEM and CONFIG_ALLOC_EXECMEM at first

config HAVE_ALLOC_EXECMEM
bool

config ALLOC_EXECMEM
bool "Executable trampline memory allocation"
depends on MODULES || HAVE_ALLOC_EXECMEM

And define fallback macro to module_alloc() like this.

#ifndef CONFIG_HAVE_ALLOC_EXECMEM
#define alloc_execmem(size, gfp) module_alloc(size)
#endif

Then, introduce a new dependency to kprobes

config KPROBES
bool "Kprobes"
select ALLOC_EXECMEM

and update kprobes to use alloc_execmem and remove module related
code from it.

You also should consider using IS_ENABLED(CONFIG_MODULE) in the code to
avoid using #ifdefs.

Finally, you can add RISCV implementation patch of HAVE_ALLOC_EXECMEM in the
next patch.

Thank you,

>
> Link: https://www.sochub.fi # for power on testing new SoC's with a minimal stack
> Link: https://lore.kernel.org/all/20220608000014.3054333-1-jarkko@profian.com/ # continuation
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> v2:
> - Better late than never right? :-)
> - Focus only to RISC-V for now to make the patch more digestable. This
> is the arch where I use the patch on a daily basis to help with QA.
> - Introduce HAVE_KPROBES_ALLOC flag to help with more gradual migration.
> ---
> arch/Kconfig | 8 +++++++-
> arch/riscv/Kconfig | 1 +
> arch/riscv/kernel/Makefile | 5 +++++
> arch/riscv/kernel/module.c | 11 -----------
> arch/riscv/kernel/module_alloc.c | 28 ++++++++++++++++++++++++++++
> kernel/kprobes.c | 10 ++++++++++
> kernel/trace/trace_kprobe.c | 18 ++++++++++++++++--
> 7 files changed, 67 insertions(+), 14 deletions(-)
> create mode 100644 arch/riscv/kernel/module_alloc.c
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index a5af0edd3eb8..c931f1de98a7 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -52,7 +52,7 @@ config GENERIC_ENTRY
>
> config KPROBES
> bool "Kprobes"
> - depends on MODULES
> + depends on MODULES || HAVE_KPROBES_ALLOC
> depends on HAVE_KPROBES
> select KALLSYMS
> select TASKS_RCU if PREEMPTION
> @@ -215,6 +215,12 @@ config HAVE_OPTPROBES
> config HAVE_KPROBES_ON_FTRACE
> bool
>
> +config HAVE_KPROBES_ALLOC
> + bool
> + help
> + Architectures that select this option are capable of allocating memory
> + for kprobes withou the kernel module allocator.
> +
> config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
> bool
> help
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e3142ce531a0..4f1b925e83d8 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -132,6 +132,7 @@ config RISCV
> select HAVE_KPROBES if !XIP_KERNEL
> select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL
> select HAVE_KRETPROBES if !XIP_KERNEL
> + select HAVE_KPROBES_ALLOC if !XIP_KERNEL
> # https://github.com/ClangBuiltLinux/linux/issues/1881
> select HAVE_LD_DEAD_CODE_DATA_ELIMINATION if !LD_IS_LLD
> select HAVE_MOVE_PMD
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index 604d6bf7e476..46318194bce1 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -73,6 +73,11 @@ obj-$(CONFIG_SMP) += cpu_ops.o
>
> obj-$(CONFIG_RISCV_BOOT_SPINWAIT) += cpu_ops_spinwait.o
> obj-$(CONFIG_MODULES) += module.o
> +ifeq ($(CONFIG_MODULES),y)
> +obj-y += module_alloc.o
> +else
> +obj-$(CONFIG_KPROBES) += module_alloc.o
> +endif
> obj-$(CONFIG_MODULE_SECTIONS) += module-sections.o
>
> obj-$(CONFIG_CPU_PM) += suspend_entry.o suspend.o
> diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
> index 5e5a82644451..cc324b450f2e 100644
> --- a/arch/riscv/kernel/module.c
> +++ b/arch/riscv/kernel/module.c
> @@ -905,17 +905,6 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
> return 0;
> }
>
> -#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
> -void *module_alloc(unsigned long size)
> -{
> - return __vmalloc_node_range(size, 1, MODULES_VADDR,
> - MODULES_END, GFP_KERNEL,
> - PAGE_KERNEL, VM_FLUSH_RESET_PERMS,
> - NUMA_NO_NODE,
> - __builtin_return_address(0));
> -}
> -#endif
> -
> int module_finalize(const Elf_Ehdr *hdr,
> const Elf_Shdr *sechdrs,
> struct module *me)
> diff --git a/arch/riscv/kernel/module_alloc.c b/arch/riscv/kernel/module_alloc.c
> new file mode 100644
> index 000000000000..3d9aa8dbca8a
> --- /dev/null
> +++ b/arch/riscv/kernel/module_alloc.c
> @@ -0,0 +1,28 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2017 Zihao Yu
> + * Copyright (c) 2024 Jarkko Sakkinen
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/moduleloader.h>
> +#include <linux/vmalloc.h>
> +#include <asm/sections.h>
> +
> +#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
> +void *module_alloc(unsigned long size)
> +{
> + return __vmalloc_node_range(size, 1, MODULES_VADDR,
> + MODULES_END, GFP_KERNEL,
> + PAGE_KERNEL, 0, NUMA_NO_NODE,
> + __builtin_return_address(0));
> +}
> +
> +void module_memfree(void *module_region)
> +{
> + if (in_interrupt())
> + pr_warn("In interrupt context: vmalloc may not work.\n");
> +
> + vfree(module_region);
> +}
> +#endif
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 9d9095e81792..2c583ab6efc4 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1580,6 +1580,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> goto out;
> }
>
> +#ifdef CONFIG_MODULES
> /* Check if 'p' is probing a module. */
> *probed_mod = __module_text_address((unsigned long) p->addr);
> if (*probed_mod) {
> @@ -1603,6 +1604,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
> ret = -ENOENT;
> }
> }
> +#endif
> +
> out:
> preempt_enable();
> jump_label_unlock();
> @@ -2482,6 +2485,7 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
> return 0;
> }
>
> +#ifdef CONFIG_MODULES
> /* Remove all symbols in given area from kprobe blacklist */
> static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
> {
> @@ -2499,6 +2503,7 @@ static void kprobe_remove_ksym_blacklist(unsigned long entry)
> {
> kprobe_remove_area_blacklist(entry, entry + 1);
> }
> +#endif /* CONFIG_MODULES */
>
> int __weak arch_kprobe_get_kallsym(unsigned int *symnum, unsigned long *value,
> char *type, char *sym)
> @@ -2564,6 +2569,7 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
> return ret ? : arch_populate_kprobe_blacklist();
> }
>
> +#ifdef CONFIG_MODULES
> static void add_module_kprobe_blacklist(struct module *mod)
> {
> unsigned long start, end;
> @@ -2665,6 +2671,7 @@ static struct notifier_block kprobe_module_nb = {
> .notifier_call = kprobes_module_callback,
> .priority = 0
> };
> +#endif /* CONFIG_MODULES */
>
> void kprobe_free_init_mem(void)
> {
> @@ -2724,8 +2731,11 @@ static int __init init_kprobes(void)
> err = arch_init_kprobes();
> if (!err)
> err = register_die_notifier(&kprobe_exceptions_nb);
> +
> +#ifdef CONFIG_MODULES
> if (!err)
> err = register_module_notifier(&kprobe_module_nb);
> +#endif
>
> kprobes_initialized = (err == 0);
> kprobe_sysctls_init();
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index c4c6e0e0068b..f8fbd5e76dda 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -111,6 +111,7 @@ static nokprobe_inline bool trace_kprobe_within_module(struct trace_kprobe *tk,
> return strncmp(module_name(mod), name, len) == 0 && name[len] == ':';
> }
>
> +#ifdef CONFIG_MODULES
> static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
> {
> char *p;
> @@ -129,6 +130,7 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
>
> return ret;
> }
> +#endif /* CONFIG_MODULES */
>
> static bool trace_kprobe_is_busy(struct dyn_event *ev)
> {
> @@ -608,7 +610,11 @@ static int append_trace_kprobe(struct trace_kprobe *tk, struct trace_kprobe *to)
>
> /* Register k*probe */
> ret = __register_trace_kprobe(tk);
> - if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
> +#ifdef CONFIG_MODULES
> + if (ret == -ENOENT && trace_kprobe_module_exist(tk))
> + ret = 0;
> +#endif /* CONFIG_MODULES */
> + if (ret == -ENOENT) {
> pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
> ret = 0;
> }
> @@ -655,7 +661,11 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
>
> /* Register k*probe */
> ret = __register_trace_kprobe(tk);
> - if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
> +#ifdef CONFIG_MODULES
> + if (ret == -ENOENT && trace_kprobe_module_exist(tk))
> + ret = 0;
> +#endif /* CONFIG_MODULES */
> + if (ret == -ENOENT) {
> pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
> ret = 0;
> }
> @@ -670,6 +680,7 @@ static int register_trace_kprobe(struct trace_kprobe *tk)
> return ret;
> }
>
> +#ifdef CONFIG_MODULES
> /* Module notifier call back, checking event on the module */
> static int trace_kprobe_module_callback(struct notifier_block *nb,
> unsigned long val, void *data)
> @@ -704,6 +715,7 @@ static struct notifier_block trace_kprobe_module_nb = {
> .notifier_call = trace_kprobe_module_callback,
> .priority = 1 /* Invoked after kprobe module callback */
> };
> +#endif /* CONFIG_MODULES */
>
> static int count_symbols(void *data, unsigned long unused)
> {
> @@ -1897,8 +1909,10 @@ static __init int init_kprobe_trace_early(void)
> if (ret)
> return ret;
>
> +#ifdef CONFIG_MODULES
> if (register_module_notifier(&trace_kprobe_module_nb))
> return -EINVAL;
> +#endif /* CONFIG_MODULES */
>
> return 0;
> }
> --
> 2.44.0
>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>