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Subject[RFC PATCH 1/5] livepatch: ftrace: arm64: Add support for DYNAMIC_FTRACE_WITH_REGS
Date
If ftrace_ops is registered with flag FTRACE_OPS_FL_SAVE_REGS, the
arch that support DYNAMIC_FTRACE_WITH_REGS will pass a full set of
pt_regs to the ftrace_ops callback function, which may read or change
the value of the pt_regs and the pt_regs will be restored to support
work flow redirection such as kernel live patching.

This patch adds DYNAMIC_FTRACE_WITH_REGS feature support for arm64
architecture.

Signed-off-by: Li Bin <huawei.libin@huawei.com>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/ftrace.h | 4 ++
arch/arm64/kernel/entry-ftrace.S | 95 ++++++++++++++++++++++++++++++++++++++
arch/arm64/kernel/ftrace.c | 28 ++++++++++-
4 files changed, 126 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7796af4..ea435c9 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -57,6 +57,7 @@ config ARM64
select HAVE_DMA_ATTRS
select HAVE_DMA_CONTIGUOUS
select HAVE_DYNAMIC_FTRACE
+ select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
select HAVE_EFFICIENT_UNALIGNED_ACCESS
select HAVE_FTRACE_MCOUNT_RECORD
select HAVE_FUNCTION_TRACER
diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index c5534fa..a7722b9 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -16,6 +16,10 @@
#define MCOUNT_ADDR ((unsigned long)_mcount)
#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE

+#ifdef CONFIG_DYNAMIC_FTRACE
+#define ARCH_SUPPORTS_FTRACE_OPS 1
+#endif
+
#ifndef __ASSEMBLY__
#include <linux/compat.h>

diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index 08cafc5..fde793b 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -12,6 +12,8 @@
#include <linux/linkage.h>
#include <asm/ftrace.h>
#include <asm/insn.h>
+#include <asm/asm-offsets.h>
+#include <asm/assembler.h>

/*
* Gcc with -pg will put the following code in the beginning of each function:
@@ -50,11 +52,37 @@
mov x29, sp
.endm

+ /* save parameter registers & corruptible registers */
+ .macro save_mcount_regs
+ sub sp, sp, #S_FRAME_SIZE
+ stp x0, x1, [sp]
+ stp x2, x3, [sp, #16]
+ stp x4, x5, [sp, #32]
+ stp x6, x7, [sp, #48]
+ stp x8, x9, [sp, #64]
+ stp x10, x11, [sp, #80]
+ stp x12, x13, [sp, #96]
+ stp x14, x15, [sp, #112]
+ .endm
+
.macro mcount_exit
ldp x29, x30, [sp], #16
ret
.endm

+ /* restore parameter registers & corruptible registers */
+ .macro restore_mcount_regs
+ ldp x0, x1, [sp]
+ ldp x2, x3, [sp, #16]
+ ldp x4, x5, [sp, #32]
+ ldp x6, x7, [sp, #48]
+ ldp x8, x9, [sp, #64]
+ ldp x10, x11, [sp, #80]
+ ldp x12, x13, [sp, #96]
+ ldp x14, x15, [sp, #112]
+ add sp, sp, #S_FRAME_SIZE
+ .endm
+
.macro mcount_adjust_addr rd, rn
sub \rd, \rn, #AARCH64_INSN_SIZE
.endm
@@ -97,6 +125,7 @@
*/
ENTRY(_mcount)
mcount_enter
+ save_mcount_regs

adrp x0, ftrace_trace_function
ldr x2, [x0, #:lo12:ftrace_trace_function]
@@ -110,8 +139,10 @@ ENTRY(_mcount)

#ifndef CONFIG_FUNCTION_GRAPH_TRACER
skip_ftrace_call: // return;
+ restore_mcount_regs
mcount_exit // }
#else
+ restore_mcount_regs
mcount_exit // return;
// }
skip_ftrace_call:
@@ -127,6 +158,7 @@ skip_ftrace_call:
cmp x0, x2
b.ne ftrace_graph_caller // ftrace_graph_caller();

+ restore_mcount_regs
mcount_exit
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
ENDPROC(_mcount)
@@ -153,15 +185,20 @@ ENDPROC(_mcount)
*/
ENTRY(ftrace_caller)
mcount_enter
+ save_mcount_regs

+ adrp x0, function_trace_op
+ ldr x2, [x0, #:lo12:function_trace_op]
mcount_get_pc0 x0 // function's pc
mcount_get_lr x1 // function's lr
+ mov x3, #0

.global ftrace_call
ftrace_call: // tracer(pc, lr);
nop // This will be replaced with "bl xxx"
// where xxx can be any kind of tracer.

+ftrace_return:
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.global ftrace_graph_call
ftrace_graph_call: // ftrace_graph_caller();
@@ -169,8 +206,65 @@ ftrace_graph_call: // ftrace_graph_caller();
// "b ftrace_graph_caller"
#endif

+ restore_mcount_regs
mcount_exit
ENDPROC(ftrace_caller)
+
+ENTRY(ftrace_regs_caller)
+ mcount_enter
+ save_mcount_regs
+
+ /* Save the rest of pt_regs */
+ stp x16, x17, [sp, #128]
+ stp x18, x19, [sp, #144]
+ stp x20, x21, [sp, #160]
+ stp x22, x23, [sp, #176]
+ stp x24, x25, [sp, #192]
+ stp x26, x27, [sp, #208]
+ stp x28, x29, [sp, #224]
+ str x30, [sp, #S_LR]
+
+ /* Save sp before profile calling */
+ add x9, sp, #S_FRAME_SIZE + 16
+ str x9, [sp, #S_SP]
+
+ /* PC of pt_regs saving lr, and can be changed by handler */
+ str x30, [sp, #S_PC]
+
+ /* Save flags */
+ mrs x9, spsr_el1
+ str x9, [sp, #S_PSTATE]
+
+ adrp x0, function_trace_op
+ ldr x2, [x0, #:lo12:function_trace_op]
+ mcount_get_pc0 x0 // function's pc
+ mcount_get_lr x1 // function's lr
+ mov x3, sp
+
+ .global ftrace_regs_call
+ftrace_regs_call: // tracer(pc, lr);
+ nop // This will be replaced with "bl xxx"
+ // where xxx can be any kind of tracer.
+ /* Handlers can change the PC */
+ ldr x9, [sp, #S_PC]
+ str x9, [x29, #8]
+
+ /* Restore the rest of pt_regs */
+ ldp x16, x17, [sp, #128]
+ ldp x18, x19, [sp, #144]
+ ldp x20, x21, [sp, #160]
+ ldp x22, x23, [sp, #176]
+ ldp x24, x25, [sp, #192]
+ ldp x26, x27, [sp, #208]
+ ldr x28, [sp, #224]
+ /* x29 & x30 should be restored by mcount_exit*/
+
+ /* Restore flags */
+ ldr x9, [sp, #S_PSTATE]
+ msr spsr_el1, x9
+
+ b ftrace_return
+ENDPROC(ftrace_regs_caller)
#endif /* CONFIG_DYNAMIC_FTRACE */

ENTRY(ftrace_stub)
@@ -193,6 +287,7 @@ ENTRY(ftrace_graph_caller)
mcount_get_parent_fp x2 // parent's fp
bl prepare_ftrace_return // prepare_ftrace_return(&lr, pc, fp)

+ restore_mcount_regs
mcount_exit
ENDPROC(ftrace_graph_caller)

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index c851be7..07175bd 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -56,12 +56,24 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
{
unsigned long pc;
u32 new;
+ int ret;

pc = (unsigned long)&ftrace_call;
new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
- AARCH64_INSN_BRANCH_LINK);
+ AARCH64_INSN_BRANCH_LINK);

- return ftrace_modify_code(pc, 0, new, false);
+ ret = ftrace_modify_code(pc, 0, new, false);
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+ if (!ret) {
+ pc = (unsigned long)&ftrace_regs_call;
+ new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
+ AARCH64_INSN_BRANCH_LINK);
+
+ ret = ftrace_modify_code(pc, 0, new, false);
+ }
+#endif
+ return ret;
}

/*
@@ -78,6 +90,18 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
return ftrace_modify_code(pc, old, new, true);
}

+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+ unsigned long addr)
+{
+ unsigned long pc = rec->ip;
+ u32 old, new;
+
+ old = aarch64_insn_gen_branch_imm(pc, old_addr, true);
+ new = aarch64_insn_gen_branch_imm(pc, addr, true);
+
+ return ftrace_modify_code(pc, old, new, true);
+}
+
/*
* Turn off the call to ftrace_caller() in instrumented function
*/
--
1.7.1


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