[tip: x86/core] x86/ftrace: Make it call depth tracking aware

From: tip-bot2 for Peter Zijlstra
Date: Mon Oct 17 2022 - 10:54:03 EST

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The following commit has been merged into the x86/core branch of tip:

Commit-ID: ee3e2469b3463d28ca4cde20e0283319ac6a562d
Gitweb: https://git.kernel.org/tip/ee3e2469b3463d28ca4cde20e0283319ac6a562d
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 15 Sep 2022 13:11:37 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 17 Oct 2022 16:41:19 +02:00

x86/ftrace: Make it call depth tracking aware

Since ftrace has trampolines, don't use thunks for the __fentry__ site
but instead require that every function called from there includes
accounting. This very much includes all the direct-call functions.

Additionally, ftrace uses ROP tricks in two places:

- return_to_handler(), and
- ftrace_regs_caller() when pt_regs->orig_ax is set by a direct-call.

return_to_handler() already uses a retpoline to replace an
indirect-jump to defeat IBT, since this is a jump-type retpoline, make
sure there is no accounting done and ALTERNATIVE the RET into a ret.

ftrace_regs_caller() does much the same and gets the same treatment.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220915111148.927545073@xxxxxxxxxxxxx
---
arch/x86/include/asm/nospec-branch.h | 9 ++++++++-
arch/x86/kernel/callthunks.c | 2 +-
arch/x86/kernel/ftrace.c | 16 +++++++++++----
arch/x86/kernel/ftrace_64.S | 22 ++++++++++++++++++--
arch/x86/net/bpf_jit_comp.c | 6 +++++-
kernel/trace/trace_selftest.c | 9 +++++++-
samples/ftrace/ftrace-direct-modify.c | 3 +++-
samples/ftrace/ftrace-direct-multi-modify.c | 3 +++-
samples/ftrace/ftrace-direct-multi.c | 2 ++-
samples/ftrace/ftrace-direct-too.c | 2 ++-
samples/ftrace/ftrace-direct.c | 2 ++-
11 files changed, 68 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 4771147..82580ad 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -343,6 +343,12 @@ static inline void x86_set_skl_return_thunk(void)
{
x86_return_thunk = &__x86_return_skl;
}
+
+#define CALL_DEPTH_ACCOUNT \
+ ALTERNATIVE("", \
+ __stringify(INCREMENT_CALL_DEPTH), \
+ X86_FEATURE_CALL_DEPTH)
+
#ifdef CONFIG_CALL_THUNKS_DEBUG
DECLARE_PER_CPU(u64, __x86_call_count);
DECLARE_PER_CPU(u64, __x86_ret_count);
@@ -351,6 +357,9 @@ DECLARE_PER_CPU(u64, __x86_ctxsw_count);
#endif
#else
static inline void x86_set_skl_return_thunk(void) {}
+
+#define CALL_DEPTH_ACCOUNT ""
+
#endif

#ifdef CONFIG_RETPOLINE
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index a03d646..7d2c75e 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -316,7 +316,7 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func)
return 0;

/* Is function call target a thunk? */
- if (is_callthunk(func))
+ if (func && is_callthunk(func))
return 0;

memcpy(*pprog, tmpl, tmpl_size);
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 4ac6692..cf15ef5 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -69,6 +69,10 @@ static const char *ftrace_nop_replace(void)

static const char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
+ /*
+ * No need to translate into a callthunk. The trampoline does
+ * the depth accounting itself.
+ */
return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void *)addr);
}

@@ -317,7 +321,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
unsigned long size;
unsigned long *ptr;
void *trampoline;
- void *ip;
+ void *ip, *dest;
/* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */
unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 };
unsigned const char retq[] = { RET_INSN_OPCODE, INT3_INSN_OPCODE };
@@ -404,10 +408,14 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
/* put in the call to the function */
mutex_lock(&text_mutex);
call_offset -= start_offset;
+ /*
+ * No need to translate into a callthunk. The trampoline does
+ * the depth accounting before the call already.
+ */
+ dest = ftrace_ops_get_func(ops);
memcpy(trampoline + call_offset,
- text_gen_insn(CALL_INSN_OPCODE,
- trampoline + call_offset,
- ftrace_ops_get_func(ops)), CALL_INSN_SIZE);
+ text_gen_insn(CALL_INSN_OPCODE, trampoline + call_offset, dest),
+ CALL_INSN_SIZE);
mutex_unlock(&text_mutex);

/* ALLOC_TRAMP flags lets us know we created it */
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index b5b54f5..6a7e6d6 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -4,6 +4,7 @@
*/

#include <linux/linkage.h>
+#include <asm/asm-offsets.h>
#include <asm/ptrace.h>
#include <asm/ftrace.h>
#include <asm/export.h>
@@ -132,6 +133,7 @@
#ifdef CONFIG_DYNAMIC_FTRACE

SYM_FUNC_START(__fentry__)
+ CALL_DEPTH_ACCOUNT
RET
SYM_FUNC_END(__fentry__)
EXPORT_SYMBOL(__fentry__)
@@ -140,6 +142,8 @@ SYM_FUNC_START(ftrace_caller)
/* save_mcount_regs fills in first two parameters */
save_mcount_regs

+ CALL_DEPTH_ACCOUNT
+
/* Stack - skipping return address of ftrace_caller */
leaq MCOUNT_REG_SIZE+8(%rsp), %rcx
movq %rcx, RSP(%rsp)
@@ -155,6 +159,9 @@ SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
/* Only ops with REGS flag set should have CS register set */
movq $0, CS(%rsp)

+ /* Account for the function call below */
+ CALL_DEPTH_ACCOUNT
+
SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
call ftrace_stub
@@ -189,6 +196,8 @@ SYM_FUNC_START(ftrace_regs_caller)
save_mcount_regs 8
/* save_mcount_regs fills in first two parameters */

+ CALL_DEPTH_ACCOUNT
+
SYM_INNER_LABEL(ftrace_regs_caller_op_ptr, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
/* Load the ftrace_ops into the 3rd parameter */
@@ -219,6 +228,9 @@ SYM_INNER_LABEL(ftrace_regs_caller_op_ptr, SYM_L_GLOBAL)
/* regs go into 4th parameter */
leaq (%rsp), %rcx

+ /* Account for the function call below */
+ CALL_DEPTH_ACCOUNT
+
SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
call ftrace_stub
@@ -282,7 +294,9 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
int3
.Ldo_rebalance:
add $8, %rsp
- RET
+ ALTERNATIVE __stringify(RET), \
+ __stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
+ X86_FEATURE_CALL_DEPTH

SYM_FUNC_END(ftrace_regs_caller)
STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)
@@ -291,6 +305,8 @@ STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)
#else /* ! CONFIG_DYNAMIC_FTRACE */

SYM_FUNC_START(__fentry__)
+ CALL_DEPTH_ACCOUNT
+
cmpq $ftrace_stub, ftrace_trace_function
jnz trace

@@ -347,6 +363,8 @@ SYM_CODE_START(return_to_handler)
int3
.Ldo_rop:
mov %rdi, (%rsp)
- RET
+ ALTERNATIVE __stringify(RET), \
+ __stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
+ X86_FEATURE_CALL_DEPTH
SYM_CODE_END(return_to_handler)
#endif
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index a6b4674..f46b620 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -12,6 +12,7 @@
#include <linux/memory.h>
#include <linux/sort.h>
#include <asm/extable.h>
+#include <asm/ftrace.h>
#include <asm/set_memory.h>
#include <asm/nospec-branch.h>
#include <asm/text-patching.h>
@@ -2135,6 +2136,11 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
prog = image;

EMIT_ENDBR();
+ /*
+ * This is the direct-call trampoline, as such it needs accounting
+ * for the __fentry__ call.
+ */
+ x86_call_depth_emit_accounting(&prog, NULL);
EMIT1(0x55); /* push rbp */
EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */
EMIT4(0x48, 0x83, 0xEC, stack_size); /* sub rsp, stack_size */
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index a2d301f..ff0536c 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -785,7 +785,14 @@ static struct fgraph_ops fgraph_ops __initdata = {
};

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
-noinline __noclone static void trace_direct_tramp(void) { }
+#ifndef CALL_DEPTH_ACCOUNT
+#define CALL_DEPTH_ACCOUNT ""
+#endif
+
+noinline __noclone static void trace_direct_tramp(void)
+{
+ asm(CALL_DEPTH_ACCOUNT);
+}
#endif

/*
diff --git a/samples/ftrace/ftrace-direct-modify.c b/samples/ftrace/ftrace-direct-modify.c
index 39146fa..de5a0f6 100644
--- a/samples/ftrace/ftrace-direct-modify.c
+++ b/samples/ftrace/ftrace-direct-modify.c
@@ -3,6 +3,7 @@
#include <linux/kthread.h>
#include <linux/ftrace.h>
#include <asm/asm-offsets.h>
+#include <asm/nospec-branch.h>

extern void my_direct_func1(void);
extern void my_direct_func2(void);
@@ -34,6 +35,7 @@ asm (
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
+ CALL_DEPTH_ACCOUNT
" call my_direct_func1\n"
" leave\n"
" .size my_tramp1, .-my_tramp1\n"
@@ -45,6 +47,7 @@ asm (
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
+ CALL_DEPTH_ACCOUNT
" call my_direct_func2\n"
" leave\n"
ASM_RET
diff --git a/samples/ftrace/ftrace-direct-multi-modify.c b/samples/ftrace/ftrace-direct-multi-modify.c
index 65aa94d..d52370c 100644
--- a/samples/ftrace/ftrace-direct-multi-modify.c
+++ b/samples/ftrace/ftrace-direct-multi-modify.c
@@ -3,6 +3,7 @@
#include <linux/kthread.h>
#include <linux/ftrace.h>
#include <asm/asm-offsets.h>
+#include <asm/nospec-branch.h>

extern void my_direct_func1(unsigned long ip);
extern void my_direct_func2(unsigned long ip);
@@ -32,6 +33,7 @@ asm (
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
+ CALL_DEPTH_ACCOUNT
" pushq %rdi\n"
" movq 8(%rbp), %rdi\n"
" call my_direct_func1\n"
@@ -46,6 +48,7 @@ asm (
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
+ CALL_DEPTH_ACCOUNT
" pushq %rdi\n"
" movq 8(%rbp), %rdi\n"
" call my_direct_func2\n"
diff --git a/samples/ftrace/ftrace-direct-multi.c b/samples/ftrace/ftrace-direct-multi.c
index 41ded7c..ec10889 100644
--- a/samples/ftrace/ftrace-direct-multi.c
+++ b/samples/ftrace/ftrace-direct-multi.c
@@ -5,6 +5,7 @@
#include <linux/ftrace.h>
#include <linux/sched/stat.h>
#include <asm/asm-offsets.h>
+#include <asm/nospec-branch.h>

extern void my_direct_func(unsigned long ip);

@@ -27,6 +28,7 @@ asm (
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
+ CALL_DEPTH_ACCOUNT
" pushq %rdi\n"
" movq 8(%rbp), %rdi\n"
" call my_direct_func\n"
diff --git a/samples/ftrace/ftrace-direct-too.c b/samples/ftrace/ftrace-direct-too.c
index 6690468..e13fb59 100644
--- a/samples/ftrace/ftrace-direct-too.c
+++ b/samples/ftrace/ftrace-direct-too.c
@@ -4,6 +4,7 @@
#include <linux/mm.h> /* for handle_mm_fault() */
#include <linux/ftrace.h>
#include <asm/asm-offsets.h>
+#include <asm/nospec-branch.h>

extern void my_direct_func(struct vm_area_struct *vma,
unsigned long address, unsigned int flags);
@@ -29,6 +30,7 @@ asm (
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
+ CALL_DEPTH_ACCOUNT
" pushq %rdi\n"
" pushq %rsi\n"
" pushq %rdx\n"
diff --git a/samples/ftrace/ftrace-direct.c b/samples/ftrace/ftrace-direct.c
index e8f1e44..1f769d0 100644
--- a/samples/ftrace/ftrace-direct.c
+++ b/samples/ftrace/ftrace-direct.c
@@ -4,6 +4,7 @@
#include <linux/sched.h> /* for wake_up_process() */
#include <linux/ftrace.h>
#include <asm/asm-offsets.h>
+#include <asm/nospec-branch.h>

extern void my_direct_func(struct task_struct *p);

@@ -26,6 +27,7 @@ asm (
ASM_ENDBR
" pushq %rbp\n"
" movq %rsp, %rbp\n"
+ CALL_DEPTH_ACCOUNT
" pushq %rdi\n"
" call my_direct_func\n"
" popq %rdi\n"

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