[PATCH v19 13/19] fprobe: Add fprobe_header encoding feature

Masami Hiramatsu (Google)
2024-11-10T15:51:34Z

Fprobe store its data structure address and size on the fgraph return stack
by __fprobe_header. But most 64bit architecture can combine those to
one unsigned long value because 4 MSB in the kernel address are the same.
With this encoding, fprobe can consume less space on ret_stack.

This introduces asm/fprobe.h to define arch dependent encode/decode
macros. Note that since fprobe depends on CONFIG_HAVE_FUNCTION_GRAPH_FREGS,
currently only arm64, loongarch, riscv, s390 and x86 are supported.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
Changes in v19:
- Fix to use Kbuild for generic arm/fprobe.h
- Check CONFIG_64BIT in asm-generic/fprobe.h.
---
arch/arm64/include/asm/Kbuild | 1 +
arch/loongarch/include/asm/fprobe.h | 12 +++++++++
arch/riscv/include/asm/Kbuild | 1 +
arch/s390/include/asm/fprobe.h | 10 ++++++++
arch/x86/include/asm/Kbuild | 1 +
include/asm-generic/fprobe.h | 46 +++++++++++++++++++++++++++++++++++
kernel/trace/fprobe.c | 29 ++++++++++++++++++++++
7 files changed, 100 insertions(+)
create mode 100644 arch/loongarch/include/asm/fprobe.h
create mode 100644 arch/s390/include/asm/fprobe.h
create mode 100644 include/asm-generic/fprobe.h

diff --git a/arch/arm64/include/asm/Kbuild b/arch/arm64/include/asm/Kbuild
index 4e350df9a02d..d2ff8f6c3231 100644
--- a/arch/arm64/include/asm/Kbuild
+++ b/arch/arm64/include/asm/Kbuild
@@ -8,6 +8,7 @@ syscall-y += unistd_32.h
syscall-y += unistd_compat_32.h

generic-y += early_ioremap.h
+generic-y += fprobe.h
generic-y += mcs_spinlock.h
generic-y += mmzone.h
generic-y += qrwlock.h
diff --git a/arch/loongarch/include/asm/fprobe.h b/arch/loongarch/include/asm/fprobe.h
new file mode 100644
index 000000000000..7af3b3126caf
--- /dev/null
+++ b/arch/loongarch/include/asm/fprobe.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_LOONGARCH_FPROBE_H
+#define _ASM_LOONGARCH_FPROBE_H
+
+/*
+ * Explicitly undef ARCH_DEFINE_ENCODE_FPROBE_HEADER, because loongarch does not
+ * have enough number of fixed MSBs of the address of kernel objects for
+ * encoding the size of data in fprobe_header. Use 2-entries encoding instead.
+ */
+#undef ARCH_DEFINE_ENCODE_FPROBE_HEADER
+
+#endif /* _ASM_LOONGARCH_FPROBE_H */
diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 1461af12da6e..e4c8790d728a 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -4,6 +4,7 @@ syscall-y += syscall_table_64.h

generic-y += early_ioremap.h
generic-y += flat.h
+generic-y += fprobe.h
generic-y += kvm_para.h
generic-y += mmzone.h
generic-y += parport.h
diff --git a/arch/s390/include/asm/fprobe.h b/arch/s390/include/asm/fprobe.h
new file mode 100644
index 000000000000..5ef600b372f4
--- /dev/null
+++ b/arch/s390/include/asm/fprobe.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_FPROBE_H
+#define _ASM_S390_FPROBE_H
+
+#include <asm-generic/fprobe.h>
+
+#undef FPROBE_HEADER_MSB_PATTERN
+#define FPROBE_HEADER_MSB_PATTERN 0
+
+#endif /* _ASM_S390_FPROBE_H */
diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
index 6c23d1661b17..58f4ddecc5fa 100644
--- a/arch/x86/include/asm/Kbuild
+++ b/arch/x86/include/asm/Kbuild
@@ -10,5 +10,6 @@ generated-y += unistd_64_x32.h
generated-y += xen-hypercalls.h

generic-y += early_ioremap.h
+generic-y += fprobe.h
generic-y += mcs_spinlock.h
generic-y += mmzone.h
diff --git a/include/asm-generic/fprobe.h b/include/asm-generic/fprobe.h
new file mode 100644
index 000000000000..8659a4dc6eb6
--- /dev/null
+++ b/include/asm-generic/fprobe.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Generic arch dependent fprobe macros.
+ */
+#ifndef __ASM_GENERIC_FPROBE_H__
+#define __ASM_GENERIC_FPROBE_H__
+
+#include <linux/bits.h>
+
+#ifdef CONFIG_64BIT
+/*
+ * Encoding the size and the address of fprobe into one 64bit entry.
+ * The 32bit architectures should use 2 entries to store those info.
+ */
+
+#define ARCH_DEFINE_ENCODE_FPROBE_HEADER
+
+#define FPROBE_HEADER_MSB_SIZE_SHIFT (BITS_PER_LONG - FPROBE_DATA_SIZE_BITS)
+#define FPROBE_HEADER_MSB_MASK \
+ GENMASK(FPROBE_HEADER_MSB_SIZE_SHIFT - 1, 0)
+
+/*
+ * By default, this expects the MSBs in the address of kprobe is 0xf.
+ * If any arch needs another fixed pattern (e.g. s390 is zero filled),
+ * override this.
+ */
+#define FPROBE_HEADER_MSB_PATTERN \
+ GENMASK(BITS_PER_LONG - 1, FPROBE_HEADER_MSB_SIZE_SHIFT)
+
+#define arch_fprobe_header_encodable(fp) \
+ (((unsigned long)(fp) & ~FPROBE_HEADER_MSB_MASK) == \
+ FPROBE_HEADER_MSB_PATTERN)
+
+#define arch_encode_fprobe_header(fp, size) \
+ (((unsigned long)(fp) & FPROBE_HEADER_MSB_MASK) | \
+ ((unsigned long)(size) << FPROBE_HEADER_MSB_SIZE_SHIFT))
+
+#define arch_decode_fprobe_header_size(val) \
+ ((unsigned long)(val) >> FPROBE_HEADER_MSB_SIZE_SHIFT)
+
+#define arch_decode_fprobe_header_fp(val) \
+ ((struct fprobe *)(((unsigned long)(val) & FPROBE_HEADER_MSB_MASK) | \
+ FPROBE_HEADER_MSB_PATTERN))
+#endif /* CONFIG_64BIT */
+
+#endif /* __ASM_GENERIC_FPROBE_H__ */
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index ed9c1d79426a..2560b312ad57 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -13,6 +13,8 @@
#include <linux/slab.h>
#include <linux/sort.h>

+#include <asm/fprobe.h>
+
#include "trace.h"

#define FPROBE_IP_HASH_BITS 8
@@ -143,6 +145,31 @@ static int del_fprobe_hash(struct fprobe *fp)
return 0;
}

+#ifdef ARCH_DEFINE_ENCODE_FPROBE_HEADER
+
+/* The arch should encode fprobe_header info into one unsigned long */
+#define FPROBE_HEADER_SIZE_IN_LONG 1
+
+static inline bool write_fprobe_header(unsigned long *stack,
+ struct fprobe *fp, unsigned int size_words)
+{
+ if (WARN_ON_ONCE(size_words > MAX_FPROBE_DATA_SIZE_WORD ||
+ !arch_fprobe_header_encodable(fp)))
+ return false;
+
+ *stack = arch_encode_fprobe_header(fp, size_words);
+ return true;
+}
+
+static inline void read_fprobe_header(unsigned long *stack,
+ struct fprobe **fp, unsigned int *size_words)
+{
+ *fp = arch_decode_fprobe_header_fp(*stack);
+ *size_words = arch_decode_fprobe_header_size(*stack);
+}
+
+#else
+
/* Generic fprobe_header */
struct __fprobe_header {
struct fprobe *fp;
@@ -173,6 +200,8 @@ static inline void read_fprobe_header(unsigned long *stack,
*size_words = fph->size_words;
}

+#endif
+
/*
* fprobe shadow stack management:
* Since fprobe shares a single fgraph_ops, it needs to share the stack entry