Re: [PATCH v2 3/4] kprobes/treewide: Explicitly override alloc/free functions

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Wed Apr 3, 2024 at 6:01 PM EEST, Mark Rutland wrote:
> Currently architectures can override kprobes_alloc_insn_page(), but
> kprobes_free_insn_page() is always implemented using module_memfree(),
> which might not be what an architecture needs, especially as we'd like
> to make it possible to use kprobes without requiring MODULES.
>
> It would be nicer if architectures either:
>
> (a) Used only the generic kprobes_alloc_insn_page() and
>     kprobes_free_insn_page(), implicitly depending on MODULES.
>
> (b) Provided their own implementation of both kprobes_alloc_insn_page()
>     and kprobes_free_insn_page(), handling the relevant dependencies
>     themselves.
>
> This patch applies that split treewide:
>
> (a) Architectures using the generic kprobes_free_insn_page() and
>     kprobes_free_insn_page() are left as-is. The __weak annotation is
>     removed from the generic implementations so that accidental
>     overrides/misuse can be detected easily.
>
> (b) Architectures which provide their own kprobes_free_insn_page() are
>     given a matching implementation of kprobes_free_insn_page(), and
>     select HAVE_KPROBES_ALLOC.
>
>     This new Kconfig symbol will allow subsequent patches to relax the
>     dependency on MODULES to (MODULES || HAVE_KPROBES_ALLOC) once other
>     module dependencies in the core kprobes code are cleaned up.
>
>     Architectures which use module_alloc() are given an implementation
>     using module_memfree() along with an explicit dependency on MODULES.
>
>     Architectures using __vmalloc_node_range() are given an
>     implementation using vfree(). This loses the warning for
>     in_interrupt(), but vfree() can handle this via vfree_atomic(), so
>     the warning isn't necessary.
>
>     On riscv, the allocator depends on !XIP_KERNEL, which is already a
>     dependency for HAVE_KPROBES in arch/riscv/Kconfig.
>
> As of this patch arm64 and riscv have kprobe allocation functions which
> do not explicitly depend on MODULES. The core kprobes code still depends
> on MODULES.
>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Albert Ou <aou@eecs.berkeley.edu>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Jarkko Sakkinen <jarkko@kernel.org>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> Cc: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Will Deacon <will@kernel.org>
> ---
>  arch/Kconfig                       | 3 +++
>  arch/arm64/Kconfig                 | 1 +
>  arch/arm64/kernel/probes/kprobes.c | 5 +++++
>  arch/powerpc/Kconfig               | 3 ++-
>  arch/powerpc/kernel/kprobes.c      | 5 +++++
>  arch/riscv/Kconfig                 | 1 +
>  arch/riscv/kernel/probes/kprobes.c | 5 +++++
>  arch/s390/Kconfig                  | 3 ++-
>  arch/s390/kernel/kprobes.c         | 5 +++++
>  arch/x86/Kconfig                   | 3 ++-
>  arch/x86/kernel/kprobes/core.c     | 5 +++++
>  include/linux/kprobes.h            | 1 +
>  kernel/kprobes.c                   | 6 ++++--
>  13 files changed, 41 insertions(+), 5 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 9f066785bb71d..85bb59f7b8c07 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -206,6 +206,9 @@ config HAVE_IOREMAP_PROT
>  config HAVE_KPROBES
>  	bool
>  
> +config HAVE_KPROBES_ALLOC
> +	bool
> +
>  config HAVE_KRETPROBES
>  	bool
>  
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7b11c98b3e84b..bda7913d6c9b8 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -233,6 +233,7 @@ config ARM64
>  	select HAVE_STACKPROTECTOR
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select HAVE_KPROBES
> +	select HAVE_KPROBES_ALLOC
>  	select HAVE_KRETPROBES
>  	select HAVE_GENERIC_VDSO
>  	select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 4b6ab7b1fa211..69d19a390cd48 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -136,6 +136,11 @@ void *kprobes_alloc_insn_page(void)
>  			NUMA_NO_NODE, __builtin_return_address(0));
>  }
>  
> +void kprobes_free_insn_page(void *page)
> +{
> +	vfree(page);
> +}
> +
>  /* arm kprobe: install breakpoint in text */
>  void __kprobes arch_arm_kprobe(struct kprobe *p)
>  {
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 1c4be33736860..13e0fc51dcdcf 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -254,7 +254,8 @@ config PPC
>  	select HAVE_KERNEL_LZMA			if DEFAULT_UIMAGE
>  	select HAVE_KERNEL_LZO			if DEFAULT_UIMAGE
>  	select HAVE_KERNEL_XZ			if PPC_BOOK3S || 44x
> -	select HAVE_KPROBES
> +	select HAVE_KPROBES			if MODULES
> +	select HAVE_KPROBES_ALLOC
>  	select HAVE_KPROBES_ON_FTRACE
>  	select HAVE_KRETPROBES
>  	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION if HAVE_OBJTOOL_MCOUNT && (!ARCH_USING_PATCHABLE_FUNCTION_ENTRY || (!CC_IS_GCC || GCC_VERSION >= 110100))
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index 0b297718d5de6..d0332aaebab09 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -146,6 +146,11 @@ void *kprobes_alloc_insn_page(void)
>  	return NULL;
>  }
>  
> +void kprobes_free_insn_page(void *page)
> +{
> +	module_memfree(page);
> +}
> +
>  int arch_prepare_kprobe(struct kprobe *p)
>  {
>  	int ret = 0;
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index be09c8836d56b..4e22549a522a5 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -139,6 +139,7 @@ config RISCV
>  	select HAVE_GENERIC_VDSO if MMU && 64BIT
>  	select HAVE_IRQ_TIME_ACCOUNTING
>  	select HAVE_KPROBES if !XIP_KERNEL
> +	select HAVE_KPROBES_ALLOC
>  	select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL
>  	select HAVE_KRETPROBES if !XIP_KERNEL
>  	# https://github.com/ClangBuiltLinux/linux/issues/1881
> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
> index 75201ce721057..37fdfa952d999 100644
> --- a/arch/riscv/kernel/probes/kprobes.c
> +++ b/arch/riscv/kernel/probes/kprobes.c
> @@ -112,6 +112,11 @@ void *kprobes_alloc_insn_page(void)
>  				     VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
>  				     __builtin_return_address(0));
>  }
> +
> +void kprobes_free_insn_page(void *page)
> +{
> +	vfree(page);
> +}
>  #endif
>  
>  /* install breakpoint in text */
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 8f01ada6845e3..635eddc3fce80 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -193,7 +193,8 @@ config S390
>  	select HAVE_KERNEL_UNCOMPRESSED
>  	select HAVE_KERNEL_XZ
>  	select HAVE_KERNEL_ZSTD
> -	select HAVE_KPROBES
> +	select HAVE_KPROBES		if MODULES
> +	select HAVE_KPROBES_ALLOC
>  	select HAVE_KPROBES_ON_FTRACE
>  	select HAVE_KRETPROBES
>  	select HAVE_LIVEPATCH
> diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
> index 91ca4d501d4ef..a5b142b8eb0f7 100644
> --- a/arch/s390/kernel/kprobes.c
> +++ b/arch/s390/kernel/kprobes.c
> @@ -45,6 +45,11 @@ void *kprobes_alloc_insn_page(void)
>  	return page;
>  }
>  
> +void kprobes_free_insn_page(void *page)
> +{
> +	module_memfree(page);
> +}
> +
>  static void *alloc_s390_insn_page(void)
>  {
>  	if (xchg(&insn_page_in_use, 1) == 1)
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 4fff6ed46e902..0810cd0bdeca9 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -240,7 +240,8 @@ config X86
>  	select HAVE_KERNEL_LZO
>  	select HAVE_KERNEL_XZ
>  	select HAVE_KERNEL_ZSTD
> -	select HAVE_KPROBES
> +	select HAVE_KPROBES			if MODULES
> +	select HAVE_KPROBES_ALLOC
>  	select HAVE_KPROBES_ON_FTRACE
>  	select HAVE_FUNCTION_ERROR_INJECTION
>  	select HAVE_KRETPROBES
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 7f01bbbfa9e2a..5f093b94d9b40 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -508,6 +508,11 @@ void *kprobes_alloc_insn_page(void)
>  	return page;
>  }
>  
> +void kprobes_free_insn_page(void *page)
> +{
> +	module_memfree(page);
> +}
> +
>  /* Kprobe x86 instruction emulation - only regs->ip or IF flag modifiers */
>  
>  static void kprobe_emulate_ifmodifiers(struct kprobe *p, struct pt_regs *regs)
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index ad4b561100f9e..651c807727bea 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -431,6 +431,7 @@ int enable_kprobe(struct kprobe *kp);
>  void dump_kprobe(struct kprobe *kp);
>  
>  void *kprobes_alloc_insn_page(void);
> +void kprobes_free_insn_page(void *page);
>  
>  void *kprobes_alloc_optinsn_page(void);
>  void kprobes_free_optinsn_page(void *page);
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 35adf56430c9b..fa2ee4e59eca2 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -110,7 +110,8 @@ enum kprobe_slot_state {
>  	SLOT_USED = 2,
>  };
>  
> -void __weak *kprobes_alloc_insn_page(void)
> +#ifndef CONFIG_HAVE_KPROBES_ALLOC
> +void *kprobes_alloc_insn_page(void)
>  {
>  	/*
>  	 * Use module_alloc() so this page is within +/- 2GB of where the
> @@ -121,10 +122,11 @@ void __weak *kprobes_alloc_insn_page(void)
>  	return module_alloc(PAGE_SIZE);
>  }
>  
> -static void kprobes_free_insn_page(void *page)
> +void kprobes_free_insn_page(void *page)
>  {
>  	module_memfree(page);
>  }
> +#endif
>  
>  struct kprobe_insn_cache kprobe_insn_slots = {
>  	.mutex = __MUTEX_INITIALIZER(kprobe_insn_slots.mutex),

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko

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