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

From: Mark Rutland
Date: Wed Apr 03 2024 - 11:03:37 EST

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@xxxxxxx>
Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
---
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),
--
2.30.2