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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [RFC v3 20/27] x86/ftrace: Adapt function tracing for PIE support
When using -fPIE/PIC with function tracing, the compiler generates a
call through the GOT (call *__fentry__@GOTPCREL). This instruction
takes 6 bytes instead of 5 on the usual relative call.
With this change, function tracing supports 6 bytes on traceable
function and can still replace relative calls on the ftrace assembly
functions.
Position Independent Executable (PIE) support will allow to extended the
KASLR randomization range below the -2G memory limit.
Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
---
arch/x86/include/asm/ftrace.h | 23 +++++-
arch/x86/include/asm/sections.h | 4 +
arch/x86/kernel/ftrace.c | 168 ++++++++++++++++++++++++++--------------
arch/x86/kernel/module.lds | 3 +
4 files changed, 139 insertions(+), 59 deletions(-)
create mode 100644 arch/x86/kernel/module.lds
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index eccd0ac6bc38..b8bbcc7fad7f 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -1,6 +1,7 @@
#ifndef _ASM_X86_FTRACE_H
#define _ASM_X86_FTRACE_H
+
#ifdef CONFIG_FUNCTION_TRACER
#ifdef CC_USING_FENTRY
# define MCOUNT_ADDR ((unsigned long)(__fentry__))
@@ -8,7 +9,19 @@
# define MCOUNT_ADDR ((unsigned long)(mcount))
# define HAVE_FUNCTION_GRAPH_FP_TEST
#endif
-#define MCOUNT_INSN_SIZE 5 /* sizeof mcount call */
+
+#define MCOUNT_RELINSN_SIZE 5 /* sizeof relative (call or jump) */
+#define MCOUNT_GOTCALL_SIZE 6 /* sizeof call *got */
+
+/*
+ * MCOUNT_INSN_SIZE is the highest size of instructions based on the
+ * configuration.
+ */
+#ifdef CONFIG_X86_PIE
+#define MCOUNT_INSN_SIZE MCOUNT_GOTCALL_SIZE
+#else
+#define MCOUNT_INSN_SIZE MCOUNT_RELINSN_SIZE
+#endif
#ifdef CONFIG_DYNAMIC_FTRACE
#define ARCH_SUPPORTS_FTRACE_OPS 1
@@ -17,6 +30,8 @@
#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
#ifndef __ASSEMBLY__
+#include <asm/sections.h>
+
extern void mcount(void);
extern atomic_t modifying_ftrace_code;
extern void __fentry__(void);
@@ -24,9 +39,11 @@ extern void __fentry__(void);
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
/*
- * addr is the address of the mcount call instruction.
- * recordmcount does the necessary offset calculation.
+ * addr is the address of the mcount call instruction. PIE has always a
+ * byte added to the start of the function.
*/
+ if (IS_ENABLED(CONFIG_X86_PIE))
+ addr -= 1;
return addr;
}
diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 2f75f30cb2f6..6b2d496cf1aa 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -11,4 +11,8 @@ extern struct exception_table_entry __stop___ex_table[];
extern char __end_rodata_hpage_align[];
#endif
+#if defined(CONFIG_X86_PIE)
+extern char __start_got[], __end_got[];
+#endif
+
#endif /* _ASM_X86_SECTIONS_H */
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 9bef1bbeba63..41d8c4c4306d 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -58,12 +58,17 @@ static int ftrace_calc_offset(long ip, long addr)
return (int)(addr - ip);
}
-static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
+static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr,
+ unsigned int size)
{
static union ftrace_code_union calc;
+ /* On PIE, fill the rest of the buffer with nops */
+ if (IS_ENABLED(CONFIG_X86_PIE))
+ memset(calc.code, ideal_nops[1][0], sizeof(calc.code));
+
calc.e8 = 0xe8;
- calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
+ calc.offset = ftrace_calc_offset(ip + MCOUNT_RELINSN_SIZE, addr);
/*
* No locking needed, this must be called via kstop_machine
@@ -72,6 +77,44 @@ static unsigned char *ftrace_call_replace(unsigned long ip,
unsigned long addr)
return calc.code;
}
+#ifdef CONFIG_X86_PIE
+union ftrace_code_got_union {
+ char code[MCOUNT_INSN_SIZE];
+ struct {
+ unsigned short ff15;
+ int offset;
+ } __attribute__((packed));
+};
+
+/* Used to identify a mcount GOT call on PIE */
+static unsigned char *ftrace_original_call(struct module* mod, unsigned long
ip,
+ unsigned long addr,
+ unsigned int size)
+{
+ static union ftrace_code_got_union calc;
+ unsigned long gotaddr;
+
+ calc.ff15 = 0x15ff;
+
+ gotaddr = module_find_got_entry(mod, addr);
+ if (!gotaddr) {
+ pr_err("Failed to find GOT entry for 0x%lx\n", addr);
+ return NULL;
+ }
+
+ calc.offset = ftrace_calc_offset(ip + MCOUNT_GOTCALL_SIZE, gotaddr);
+ return calc.code;
+}
+#else
+static unsigned char *ftrace_original_call(struct module* mod, unsigned long
ip,
+ unsigned long addr,
+ unsigned int size)
+{
+ return ftrace_call_replace(ip, addr, size);
+}
+
+#endif
+
static inline int
within(unsigned long addr, unsigned long start, unsigned long end)
{
@@ -94,16 +137,18 @@ static unsigned long text_ip_addr(unsigned long ip)
return ip;
}
-static const unsigned char *ftrace_nop_replace(void)
+static const unsigned char *ftrace_nop_replace(unsigned int size)
{
- return ideal_nops[NOP_ATOMIC5];
+ return ideal_nops[size == 5 ? NOP_ATOMIC5 : size];
}
static int
-ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
- unsigned const char *new_code)
+ftrace_modify_code_direct(struct dyn_ftrace *rec, unsigned const char
*old_code,
+ unsigned const char *new_code)
{
unsigned char replaced[MCOUNT_INSN_SIZE];
+ unsigned long ip = rec->ip;
+ unsigned int size = MCOUNT_INSN_SIZE;
ftrace_expected = old_code;
@@ -116,17 +161,17 @@ ftrace_modify_code_direct(unsigned long ip, unsigned
const char *old_code,
*/
/* read the text we want to modify */
- if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+ if (probe_kernel_read(replaced, (void *)ip, size))
return -EFAULT;
/* Make sure it is what we expect it to be */
- if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
+ if (memcmp(replaced, old_code, size) != 0)
return -EINVAL;
ip = text_ip_addr(ip);
/* replace the text with the new text */
- if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
+ if (probe_kernel_write((void *)ip, new_code, size))
return -EPERM;
sync_core();
@@ -139,9 +184,7 @@ int ftrace_make_nop(struct module *mod,
{
unsigned const char *new, *old;
unsigned long ip = rec->ip;
-
- old = ftrace_call_replace(ip, addr);
- new = ftrace_nop_replace();
+ unsigned int size = MCOUNT_INSN_SIZE;
/*
* On boot up, and when modules are loaded, the MCOUNT_ADDR
@@ -151,14 +194,20 @@ int ftrace_make_nop(struct module *mod,
* We do not want to use the breakpoint version in this case,
* just modify the code directly.
*/
- if (addr == MCOUNT_ADDR)
- return ftrace_modify_code_direct(rec->ip, old, new);
+ if (addr != MCOUNT_ADDR) {
+ ftrace_expected = NULL;
- ftrace_expected = NULL;
+ /* Normal cases use add_brk_on_nop */
+ WARN_ONCE(1, "invalid use of ftrace_make_nop");
+ return -EINVAL;
+ }
- /* Normal cases use add_brk_on_nop */
- WARN_ONCE(1, "invalid use of ftrace_make_nop");
- return -EINVAL;
+ old = ftrace_original_call(mod, ip, addr, size);
+ if (!old)
+ return -EINVAL;
+ new = ftrace_nop_replace(size);
+
+ return ftrace_modify_code_direct(rec, old, new);
}
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
@@ -166,11 +215,11 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned
long addr)
unsigned const char *new, *old;
unsigned long ip = rec->ip;
- old = ftrace_nop_replace();
- new = ftrace_call_replace(ip, addr);
+ old = ftrace_nop_replace(MCOUNT_INSN_SIZE);
+ new = ftrace_call_replace(ip, addr, MCOUNT_INSN_SIZE);
/* Should only be called when module is loaded */
- return ftrace_modify_code_direct(rec->ip, old, new);
+ return ftrace_modify_code_direct(rec, old, new);
}
/*
@@ -233,7 +282,7 @@ static int update_ftrace_func(unsigned long ip, void *new)
unsigned char old[MCOUNT_INSN_SIZE];
int ret;
- memcpy(old, (void *)ip, MCOUNT_INSN_SIZE);
+ memcpy(old, (void *)ip, MCOUNT_RELINSN_SIZE);
ftrace_update_func = ip;
/* Make sure the breakpoints see the ftrace_update_func update */
@@ -255,13 +304,14 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
unsigned char *new;
int ret;
- new = ftrace_call_replace(ip, (unsigned long)func);
+ new = ftrace_call_replace(ip, (unsigned long)func, MCOUNT_RELINSN_SIZE);
ret = update_ftrace_func(ip, new);
/* Also update the regs callback function */
if (!ret) {
ip = (unsigned long)(&ftrace_regs_call);
- new = ftrace_call_replace(ip, (unsigned long)func);
+ new = ftrace_call_replace(ip, (unsigned long)func,
+ MCOUNT_RELINSN_SIZE);
ret = update_ftrace_func(ip, new);
}
@@ -309,18 +359,18 @@ static int ftrace_write(unsigned long ip, const char
*val, int size)
return 0;
}
-static int add_break(unsigned long ip, const char *old)
+static int add_break(unsigned long ip, const char *old, unsigned int size)
{
unsigned char replaced[MCOUNT_INSN_SIZE];
unsigned char brk = BREAKPOINT_INSTRUCTION;
- if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+ if (probe_kernel_read(replaced, (void *)ip, size))
return -EFAULT;
ftrace_expected = old;
/* Make sure it is what we expect it to be */
- if (memcmp(replaced, old, MCOUNT_INSN_SIZE) != 0)
+ if (memcmp(replaced, old, size) != 0)
return -EINVAL;
return ftrace_write(ip, &brk, 1);
@@ -330,20 +380,22 @@ static int add_brk_on_call(struct dyn_ftrace *rec,
unsigned long addr)
{
unsigned const char *old;
unsigned long ip = rec->ip;
+ unsigned int size = MCOUNT_INSN_SIZE;
- old = ftrace_call_replace(ip, addr);
+ old = ftrace_call_replace(ip, addr, size);
- return add_break(rec->ip, old);
+ return add_break(rec->ip, old, size);
}
static int add_brk_on_nop(struct dyn_ftrace *rec)
{
unsigned const char *old;
+ unsigned int size = MCOUNT_INSN_SIZE;
- old = ftrace_nop_replace();
+ old = ftrace_nop_replace(size);
- return add_break(rec->ip, old);
+ return add_break(rec->ip, old, size);
}
static int add_breakpoints(struct dyn_ftrace *rec, int enable)
@@ -386,22 +438,23 @@ static int remove_breakpoint(struct dyn_ftrace *rec)
const unsigned char *nop;
unsigned long ftrace_addr;
unsigned long ip = rec->ip;
+ unsigned int size = MCOUNT_INSN_SIZE;
/* If we fail the read, just give up */
- if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
+ if (probe_kernel_read(ins, (void *)ip, size))
return -EFAULT;
/* If this does not have a breakpoint, we are done */
if (ins[0] != brk)
return 0;
- nop = ftrace_nop_replace();
+ nop = ftrace_nop_replace(size);
/*
* If the last 4 bytes of the instruction do not match
* a nop, then we assume that this is a call to ftrace_addr.
*/
- if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
+ if (memcmp(&ins[1], &nop[1], size - 1) != 0) {
/*
* For extra paranoidism, we check if the breakpoint is on
* a call that would actually jump to the ftrace_addr.
@@ -409,18 +462,18 @@ static int remove_breakpoint(struct dyn_ftrace *rec)
* a disaster.
*/
ftrace_addr = ftrace_get_addr_new(rec);
- nop = ftrace_call_replace(ip, ftrace_addr);
+ nop = ftrace_call_replace(ip, ftrace_addr, size);
- if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) == 0)
+ if (memcmp(&ins[1], &nop[1], size - 1) == 0)
goto update;
/* Check both ftrace_addr and ftrace_old_addr */
ftrace_addr = ftrace_get_addr_curr(rec);
- nop = ftrace_call_replace(ip, ftrace_addr);
+ nop = ftrace_call_replace(ip, ftrace_addr, size);
ftrace_expected = nop;
- if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
+ if (memcmp(&ins[1], &nop[1], size - 1) != 0)
return -EINVAL;
}
@@ -428,30 +481,33 @@ static int remove_breakpoint(struct dyn_ftrace *rec)
return ftrace_write(ip, nop, 1);
}
-static int add_update_code(unsigned long ip, unsigned const char *new)
+static int add_update_code(unsigned long ip, unsigned const char *new,
+ unsigned int size)
{
/* skip breakpoint */
ip++;
new++;
- return ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1);
+ return ftrace_write(ip, new, size - 1);
}
static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long ip = rec->ip;
+ unsigned int size = MCOUNT_INSN_SIZE;
unsigned const char *new;
- new = ftrace_call_replace(ip, addr);
- return add_update_code(ip, new);
+ new = ftrace_call_replace(ip, addr, size);
+ return add_update_code(ip, new, size);
}
static int add_update_nop(struct dyn_ftrace *rec)
{
unsigned long ip = rec->ip;
+ unsigned int size = MCOUNT_INSN_SIZE;
unsigned const char *new;
- new = ftrace_nop_replace();
- return add_update_code(ip, new);
+ new = ftrace_nop_replace(size);
+ return add_update_code(ip, new, size);
}
static int add_update(struct dyn_ftrace *rec, int enable)
@@ -485,7 +541,7 @@ static int finish_update_call(struct dyn_ftrace *rec,
unsigned long addr)
unsigned long ip = rec->ip;
unsigned const char *new;
- new = ftrace_call_replace(ip, addr);
+ new = ftrace_call_replace(ip, addr, MCOUNT_INSN_SIZE);
return ftrace_write(ip, new, 1);
}
@@ -495,7 +551,7 @@ static int finish_update_nop(struct dyn_ftrace *rec)
unsigned long ip = rec->ip;
unsigned const char *new;
- new = ftrace_nop_replace();
+ new = ftrace_nop_replace(MCOUNT_INSN_SIZE);
return ftrace_write(ip, new, 1);
}
@@ -619,13 +675,13 @@ ftrace_modify_code(unsigned long ip, unsigned const char
*old_code,
{
int ret;
- ret = add_break(ip, old_code);
+ ret = add_break(ip, old_code, MCOUNT_RELINSN_SIZE);
if (ret)
goto out;
run_sync();
- ret = add_update_code(ip, new_code);
+ ret = add_update_code(ip, new_code, MCOUNT_RELINSN_SIZE);
if (ret)
goto fail_update;
@@ -670,7 +726,7 @@ static unsigned char *ftrace_jmp_replace(unsigned long ip,
unsigned long addr)
/* Jmp not a call (ignore the .e8) */
calc.e8 = 0xe9;
- calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
+ calc.offset = ftrace_calc_offset(ip + MCOUNT_RELINSN_SIZE, addr);
/*
* ftrace external locks synchronize the access to the static variable.
@@ -766,11 +822,11 @@ create_trampoline(struct ftrace_ops *ops, unsigned int
*tramp_size)
* the jmp to ftrace_epilogue, as well as the address of
* the ftrace_ops this trampoline is used for.
*/
- trampoline = alloc_tramp(size + MCOUNT_INSN_SIZE + sizeof(void *));
+ trampoline = alloc_tramp(size + MCOUNT_RELINSN_SIZE + sizeof(void *));
if (!trampoline)
return 0;
- *tramp_size = size + MCOUNT_INSN_SIZE + sizeof(void *);
+ *tramp_size = size + MCOUNT_RELINSN_SIZE + sizeof(void *);
/* Copy ftrace_caller onto the trampoline memory */
ret = probe_kernel_read(trampoline, (void *)start_offset, size);
@@ -783,7 +839,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int
*tramp_size)
/* The trampoline ends with a jmp to ftrace_epilogue */
jmp = ftrace_jmp_replace(ip, (unsigned long)ftrace_epilogue);
- memcpy(trampoline + size, jmp, MCOUNT_INSN_SIZE);
+ memcpy(trampoline + size, jmp, MCOUNT_RELINSN_SIZE);
/*
* The address of the ftrace_ops that is used for this trampoline
@@ -793,7 +849,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int
*tramp_size)
* the global function_trace_op variable.
*/
- ptr = (unsigned long *)(trampoline + size + MCOUNT_INSN_SIZE);
+ ptr = (unsigned long *)(trampoline + size + MCOUNT_RELINSN_SIZE);
*ptr = (unsigned long)ops;
op_offset -= start_offset;
@@ -868,7 +924,7 @@ void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
func = ftrace_ops_get_func(ops);
/* Do a safe modify in case the trampoline is executing */
- new = ftrace_call_replace(ip, (unsigned long)func);
+ new = ftrace_call_replace(ip, (unsigned long)func, MCOUNT_RELINSN_SIZE);
ret = update_ftrace_func(ip, new);
set_memory_ro(ops->trampoline, npages);
@@ -882,7 +938,7 @@ static void *addr_from_call(void *ptr)
union ftrace_code_union calc;
int ret;
- ret = probe_kernel_read(&calc, ptr, MCOUNT_INSN_SIZE);
+ ret = probe_kernel_read(&calc, ptr, MCOUNT_RELINSN_SIZE);
if (WARN_ON_ONCE(ret < 0))
return NULL;
@@ -892,7 +948,7 @@ static void *addr_from_call(void *ptr)
return NULL;
}
- return ptr + MCOUNT_INSN_SIZE + calc.offset;
+ return ptr + MCOUNT_RELINSN_SIZE + calc.offset;
}
void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
diff --git a/arch/x86/kernel/module.lds b/arch/x86/kernel/module.lds
new file mode 100644
index 000000000000..fd6e95a4b454
--- /dev/null
+++ b/arch/x86/kernel/module.lds
@@ -0,0 +1,3 @@
+SECTIONS {
+ .got (NOLOAD) : { BYTE(0) }
+}
--
2.14.2.920.gcf0c67979c-goog
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