Re: [PATCH v4 3/7] vmalloc: Add text_alloc() and text_free()

[Masami Hiramatsu <mhiramat@kernel.org>]

On Sat, 18 Jul 2020 19:23:59 +0300
Mike Rapoport <rppt@kernel.org> wrote:

> On Fri, Jul 17, 2020 at 06:04:17AM +0300, Jarkko Sakkinen wrote:
> > Introduce functions for allocating memory for dynamic trampolines, such
> > as kprobes. An arch can promote the availability of these functions with
> > CONFIG_ARCH_HAS_TEXT_ALLOC. Provide default/fallback implementation
> > wrapping module_alloc() and module_memfree().
> > 
> > Cc: Andi Kleen <ak@linux.intel.com>
> > Cc: Masami Hiramatsu <mhiramat@kernel.org>
> > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> > ---
> >  include/linux/vmalloc.h | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> > 
> > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> > index 0221f852a7e1..e981436e30b6 100644
> > --- a/include/linux/vmalloc.h
> > +++ b/include/linux/vmalloc.h
> > @@ -9,6 +9,7 @@
> >  #include <asm/page.h>		/* pgprot_t */
> >  #include <linux/rbtree.h>
> >  #include <linux/overflow.h>
> > +#include <linux/moduleloader.h>
> >  
> >  #include <asm/vmalloc.h>
> >  
> > @@ -249,4 +250,26 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
> >  int register_vmap_purge_notifier(struct notifier_block *nb);
> >  int unregister_vmap_purge_notifier(struct notifier_block *nb);
> >  
> > +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC
> > +/*
> > + * Allocate memory to be used for dynamic trampoline code.
> > + */
> > +void *text_alloc(unsigned long size);
> > +
> > +/*
> > + * Free memory returned from text_alloc().
> > + */
> > +void text_free(void *region);
> > +#else
> > +static inline void *text_alloc(unsigned long size)
> > +{
> > +	return module_alloc(size);
> > +}
> > +
> > +static inline void text_free(void *region)
> > +{
> > +	module_memfree(region);
> > +}
> 
> Using module_alloc() as the default implementation of generic
> text_alloc() does not sound right to me.
> 
> I would suggest rename module_alloc() to text_alloc() on x86, as Peter
> proposed and then add text_alloc_kprobes() that can be overridden by the
> architectures. x86 could use text_alloc(), arm64 vmalloc() with options
> of their choice and the fallback would remain module_alloc(). Something
> like (untested) patch below:

Hmm, of course we need some more work on this patch (e.g. MODULE_STATE_*
for callbacks), but basically, this direction seems good to me for the
first step.
If other dynamic trampoline code (ftrace and bpf) are interested in replacing
the module_alloc() with text_alloc_*(), we should revisit how we can unify
it (or at least share the common parts.)

BTW, this changes CONFIG_MODULES dependency according to the architecture
implementation. It also should be noted somewhere.

Thank you,


> From 928b6903e76ebf5790fc415f9eed390e400e5bc3 Mon Sep 17 00:00:00 2001
> From: Mike Rapoport <rppt@linux.ibm.com>
> Date: Sat, 18 Jul 2020 19:13:02 +0300
> Subject: [PATCH] kprobes: introduce text_alloc_kprobes() and
>  text_free_kprobes()
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
>  arch/Kconfig                       |  5 ++++-
>  arch/arm64/Kconfig                 |  1 +
>  arch/arm64/kernel/probes/kprobes.c | 10 ++++++++--
>  arch/x86/Kconfig                   |  3 ++-
>  arch/x86/kernel/kprobes/core.c     |  9 ++++-----
>  include/linux/kprobes.h            | 17 +++++++++++++++--
>  kernel/kprobes.c                   |  8 ++++----
>  7 files changed, 38 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 8cc35dc556c7..c0589b3b3225 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -61,7 +61,7 @@ config OPROFILE_NMI_TIMER
>  
>  config KPROBES
>  	bool "Kprobes"
> -	depends on MODULES
> +	depends on MODULES || HAVE_KPROBES_TEXT_ALLOC
>  	depends on HAVE_KPROBES
>  	select KALLSYMS
>  	help
> @@ -186,6 +186,9 @@ config HAVE_IOREMAP_PROT
>  config HAVE_KPROBES
>  	bool
>  
> +config HAVE_KPROBES_TEXT_ALLOC
> +	bool
> +
>  config HAVE_KRETPROBES
>  	bool
>  
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 66dc41fd49f2..abc0538b13ef 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -177,6 +177,7 @@ config ARM64
>  	select HAVE_STACKPROTECTOR
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select HAVE_KPROBES
> +	select HAVE_KPROBES_TEXT_ALLOC
>  	select HAVE_KRETPROBES
>  	select HAVE_GENERIC_VDSO
>  	select IOMMU_DMA if IOMMU_SUPPORT
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 5290f17a4d80..fac8c6020040 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -118,13 +118,19 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  	return 0;
>  }
>  
> -void *alloc_insn_page(void)
> +void *text_alloc_kprobes(unsigned long size)
>  {
> -	return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
> +	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
>  			GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
>  			NUMA_NO_NODE, __builtin_return_address(0));
>  }
>  
> +void text_free_kprobes(void *mem)
> +{
> +	lockdep_assert_irqs_enabled();
> +	vfree(mem);
> +}
> +
>  /* arm kprobe: install breakpoint in text */
>  void __kprobes arch_arm_kprobe(struct kprobe *p)
>  {
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 883da0abf779..d08b92f91531 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -190,6 +190,7 @@ config X86
>  	select HAVE_KERNEL_XZ
>  	select HAVE_KPROBES
>  	select HAVE_KPROBES_ON_FTRACE
> +	select HAVE_KPROBES_TEXT_ALLOC
>  	select HAVE_FUNCTION_ERROR_INJECTION
>  	select HAVE_KRETPROBES
>  	select HAVE_KVM
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index ada39ddbc922..a3e8f01c62d4 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -418,12 +418,11 @@ static int prepare_boost(kprobe_opcode_t *buf, struct kprobe *p,
>  	return len;
>  }
>  
> -/* Make page to RO mode when allocate it */
> -void *alloc_insn_page(void)
> +void *text_alloc_kprobes(unsigned long size)
>  {
>  	void *page;
>  
> -	page = module_alloc(PAGE_SIZE);
> +	page = text_alloc(size);
>  	if (!page)
>  		return NULL;
>  
> @@ -444,9 +443,9 @@ void *alloc_insn_page(void)
>  }
>  
>  /* Recover page to RW mode before releasing it */
> -void free_insn_page(void *page)
> +void text_free_kprobes(void *page)
>  {
> -	module_memfree(page);
> +	text_free(page);
>  }
>  
>  static int arch_copy_kprobe(struct kprobe *p)
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 6adf90f248d7..dbc9c71d4ec4 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -27,6 +27,7 @@
>  #include <linux/rcupdate.h>
>  #include <linux/mutex.h>
>  #include <linux/ftrace.h>
> +#include <linux/moduleloader.h>
>  #include <asm/kprobes.h>
>  
>  #ifdef CONFIG_KPROBES
> @@ -374,8 +375,20 @@ int enable_kprobe(struct kprobe *kp);
>  
>  void dump_kprobe(struct kprobe *kp);
>  
> -void *alloc_insn_page(void);
> -void free_insn_page(void *page);
> +#ifdef CONFIG_HAVE_KPROBES_TEXT_ALLOC
> +void *text_alloc_kprobes(unsigned long size);
> +void text_free_kprobes(void *page);
> +#else
> +static inline void *text_alloc_kprobes(unsigned long size)
> +{
> +	return module_alloc(size);
> +}
> +
> +static inline void text_free_kprobes(void *page)
> +{
> +	module_memfree(page);
> +}
> +#endif
>  
>  #else /* !CONFIG_KPROBES: */
>  
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2e97febeef77..c4f107682250 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -109,14 +109,14 @@ enum kprobe_slot_state {
>  	SLOT_USED = 2,
>  };
>  
> -void __weak *alloc_insn_page(void)
> +static void *alloc_insn_page(void)
>  {
> -	return module_alloc(PAGE_SIZE);
> +	return text_alloc_kprobes(PAGE_SIZE);
>  }
>  
> -void __weak free_insn_page(void *page)
> +static void free_insn_page(void *page)
>  {
> -	module_memfree(page);
> +	text_free_kprobes(page);
>  }
>  
>  struct kprobe_insn_cache kprobe_insn_slots = {
> -- 
> 2.26.2
> 
> 
> > +#endif
> > +
> >  #endif /* _LINUX_VMALLOC_H */
> > -- 
> > 2.25.1
> > 
> 
> -- 
> Sincerely yours,
> Mike.


-- 
Masami Hiramatsu <mhiramat@kernel.org>