Message-Id: <20240325115632.04e37297491cadfbbf382767@kernel.org>
Date: Mon, 25 Mar 2024 11:56:32 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: linux-riscv@...ts.infradead.org, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou
 <aou@...s.berkeley.edu>, linux-kernel@...r.kernel.org, "Naveen N . Rao"
 <naveen.n.rao@...ux.ibm.com>, Anil S Keshavamurthy
 <anil.s.keshavamurthy@...el.com>, "David S . Miller" <davem@...emloft.net>,
 Masami Hiramatsu <mhiramat@...nel.org>, linux-trace-kernel@...r.kernel.org,
 Calvin Owens <jcalvinowens@...il.com>
Subject: Re: [PATCH v2] arch/riscv: Enable kprobes when CONFIG_MODULES=n

Hi Jarkko,

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

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