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

Calvin Owens
2024-03-25T03:58:18Z

On Monday 03/25 at 11:56 +0900, Masami Hiramatsu wrote:
> 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/

FYI, I should have v2 of that series out later this week.

Thanks,
Calvin

> 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>