[PATCH v18 12/17] fprobe: Add fprobe_header encoding feature

From: Masami Hiramatsu (Google)
Date: Sat Oct 26 2024 - 00:38:38 EST

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From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
Cc: WANG Xuerui <kernel@xxxxxxxxxx>
Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
---
arch/arm64/include/asm/fprobe.h | 7 +++++++
arch/loongarch/include/asm/fprobe.h | 5 +++++
arch/riscv/include/asm/fprobe.h | 9 +++++++++
arch/s390/include/asm/fprobe.h | 10 ++++++++++
arch/x86/include/asm/fprobe.h | 9 +++++++++
include/asm-generic/fprobe.h | 33 +++++++++++++++++++++++++++++++++
kernel/trace/fprobe.c | 29 +++++++++++++++++++++++++++++
7 files changed, 102 insertions(+)
create mode 100644 arch/arm64/include/asm/fprobe.h
create mode 100644 arch/loongarch/include/asm/fprobe.h
create mode 100644 arch/riscv/include/asm/fprobe.h
create mode 100644 arch/s390/include/asm/fprobe.h
create mode 100644 arch/x86/include/asm/fprobe.h
create mode 100644 include/asm-generic/fprobe.h

diff --git a/arch/arm64/include/asm/fprobe.h b/arch/arm64/include/asm/fprobe.h
new file mode 100644
index 000000000000..bbf254db878d
--- /dev/null
+++ b/arch/arm64/include/asm/fprobe.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARM64_FPROBE_H
+#define _ASM_ARM64_FPROBE_H
+
+#include <asm-generic/fprobe.h>
+
+#endif /* _ASM_ARM64_FPROBE_H */
\ No newline at end of file
diff --git a/arch/loongarch/include/asm/fprobe.h b/arch/loongarch/include/asm/fprobe.h
new file mode 100644
index 000000000000..68156a66873c
--- /dev/null
+++ b/arch/loongarch/include/asm/fprobe.h
@@ -0,0 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_LOONGARCH_FPROBE_H
+#define _ASM_LOONGARCH_FPROBE_H
+
+#endif /* _ASM_LOONGARCH_FPROBE_H */
\ No newline at end of file
diff --git a/arch/riscv/include/asm/fprobe.h b/arch/riscv/include/asm/fprobe.h
new file mode 100644
index 000000000000..51fc2ef3eda1
--- /dev/null
+++ b/arch/riscv/include/asm/fprobe.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_FPROBE_H
+#define _ASM_RISCV_FPROBE_H
+
+#ifdef CONFIG_64BIT
+#include <asm-generic/fprobe.h>
+#endif
+
+#endif /* _ASM_RISCV_FPROBE_H */
\ No newline at end of file
diff --git a/arch/s390/include/asm/fprobe.h b/arch/s390/include/asm/fprobe.h
new file mode 100644
index 000000000000..84b94ba6e3a4
--- /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 */
\ No newline at end of file
diff --git a/arch/x86/include/asm/fprobe.h b/arch/x86/include/asm/fprobe.h
new file mode 100644
index 000000000000..c863518bef90
--- /dev/null
+++ b/arch/x86/include/asm/fprobe.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_FPROBE_H
+#define _ASM_X86_FPROBE_H
+
+#ifdef CONFIG_64BIT
+#include <asm-generic/fprobe.h>
+#endif
+
+#endif /* _ASM_X86_FPROBE_H */
\ No newline at end of file
diff --git a/include/asm-generic/fprobe.h b/include/asm-generic/fprobe.h
new file mode 100644
index 000000000000..00f480748a1d
--- /dev/null
+++ b/include/asm-generic/fprobe.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * linux/include/asm-generic/fprobe.h
+ */
+#ifndef __ASM_GENERIC_FPROBE_H__
+#define __ASM_GENERIC_FPROBE_H__
+
+#include <linux/bits.h>
+
+#define ARCH_HAVE_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)
+#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 /* __ASM_GENERIC_FPROBE_H__ */
\ No newline at end of file
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index ed9c1d79426a..949963f1f17a 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_HAVE_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

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