When we tracing multiple functions, it has to use a list
function and cause all the other functions being traced
to check the hash of the ftrace_ops. But this is very
inefficient.
we can call a dynamically allocated trampoline which calls
the callback directly to solve this problem. This patch
introduce dynamically alloced trampolines for ARM64.
If a callback is registered to a function and there's no
other callback registered to that function, the ftrace_ops
will get its own trampoline allocated for it that will call
the function directly.
We merge two functions (ftrace_caller/ftrace_regs_caller and
ftrace_common) into one function, so we no longer need a jump
to ftrace_common and fix it to NOP.
similar to X86_64, save the local ftrace_ops at the end.
the ftrace trampoline layout :
low
ftrace_(regs_)caller => +---------------+
| ftrace_caller |
ftrace_common => +---------------+
| ftrace_common |
function_trace_op_ptr => | ... | ldr x2, <ftrace_ops>
| | b ftrace_stub |
| | nop | fgraph call
| +---------------+
+------------>| ftrace_ops |
+---------------+
| PLT entrys | (TODO)
+---------------+
high
Known issues :
If kaslr is enabled, the address of tramp and ftrace call
may be far away. Therefore, long jump support is required.
Here I intend to use the same solution as module relocating,
Reserve enough space for PLT at the end when allocating, can
use PLT to complete these long jumps.
Signed-off-by: Cheng Jian <[email protected]>
---
arch/arm64/kernel/entry-ftrace.S | 4 +
arch/arm64/kernel/ftrace.c | 310 +++++++++++++++++++++++++++++++
2 files changed, 314 insertions(+)
diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index 7d02f9966d34..f5ee797804ac 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -77,17 +77,20 @@
ENTRY(ftrace_regs_caller)
ftrace_regs_entry 1
+GLOBAL(ftrace_regs_caller_end)
b ftrace_common
ENDPROC(ftrace_regs_caller)
ENTRY(ftrace_caller)
ftrace_regs_entry 0
+GLOBAL(ftrace_caller_end)
b ftrace_common
ENDPROC(ftrace_caller)
ENTRY(ftrace_common)
sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
mov x1, x9 // parent_ip (callsite's LR)
+GLOBAL(function_trace_op_ptr)
ldr_l x2, function_trace_op // op
mov x3, sp // regs
@@ -121,6 +124,7 @@ ftrace_common_return:
/* Restore the callsite's SP */
add sp, sp, #S_FRAME_SIZE + 16
+GLOBAL(ftrace_common_end)
ret x9
ENDPROC(ftrace_common)
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 8618faa82e6d..95ea68ef6228 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -10,11 +10,13 @@
#include <linux/module.h>
#include <linux/swab.h>
#include <linux/uaccess.h>
+#include <linux/vmalloc.h>
#include <asm/cacheflush.h>
#include <asm/debug-monitors.h>
#include <asm/ftrace.h>
#include <asm/insn.h>
+#include <asm/set_memory.h>
#ifdef CONFIG_DYNAMIC_FTRACE
/*
@@ -47,6 +49,314 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
return 0;
}
+/* ftrace dynamic trampolines */
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+#ifdef CONFIG_MODULES
+#include <linux/moduleloader.h>
+
+static inline void *alloc_tramp(unsigned long size)
+{
+ return module_alloc(size);
+}
+
+static inline void tramp_free(void *tramp)
+{
+ module_memfree(tramp);
+}
+#else
+static inline void *alloc_tramp(unsigned long size)
+{
+ return NULL;
+}
+
+static inline void tramp_free(void *tramp) {}
+#endif
+
+extern void ftrace_regs_caller_end(void);
+extern void ftrace_caller_end(void);
+extern void ftrace_common(void);
+extern void ftrace_common_end(void);
+
+extern void function_trace_op_ptr(void);
+
+extern struct ftrace_ops *function_trace_op;
+
+/*
+ * ftrace_caller() or ftrace_regs_caller() trampoline
+ * +-----------------------+
+ * ftrace_(regs_)caller => | ...... |
+ * ftrace_(regs_)caller_end => | b ftrace_common | => nop
+ * +-----------------------+
+ * ftrace_common => | ...... |
+ * function_trace_op_ptr => | adrp x2, sym | => nop
+ * | ldr x2,[x2,:lo12:sym]| => ldr x2 <ftrace_op>
+ * | ...... |
+ * ftrace_common_end => | retq |
+ * +-----------------------+
+ * ftrace_opt => | ftrace_opt |
+ * +-----------------------+
+ */
+static unsigned long create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
+{
+ unsigned long start_offset_caller, end_offset_caller, caller_size;
+ unsigned long start_offset_common, end_offset_common, common_size;
+ unsigned long op_offset, offset, size, ip, npages;
+ void *trampoline;
+ unsigned long *ptr;
+ /* ldr x2, <label> */
+ u32 pc_ldr = 0x58000002;
+ u32 mask = BIT(19) - 1;
+ int shift = 5;
+ int ret;
+ u32 nop;
+
+ if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
+ start_offset_caller = (unsigned long)ftrace_regs_caller;
+ end_offset_caller = (unsigned long)ftrace_regs_caller_end;
+ } else {
+ start_offset_caller = (unsigned long)ftrace_caller;
+ end_offset_caller = (unsigned long)ftrace_caller_end;
+ }
+ start_offset_common = (unsigned long)ftrace_common;
+ end_offset_common = (unsigned long)ftrace_common_end;
+
+ op_offset = (unsigned long)function_trace_op_ptr;
+
+ /*
+ * Merge ftrace_caller/ftrace_regs_caller and ftrace_common
+ * to one function in ftrace trampoline.
+ */
+ caller_size = end_offset_caller - start_offset_caller + AARCH64_INSN_SIZE;
+ common_size = end_offset_common - start_offset_common + AARCH64_INSN_SIZE;
+ size = caller_size + common_size;
+
+ trampoline = alloc_tramp(caller_size + common_size + sizeof(void *));
+ if (!trampoline)
+ return 0;
+
+ *tramp_size = caller_size + common_size + sizeof(void *);
+ npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
+
+ /* Copy ftrace_caller/ftrace_regs_caller onto the trampoline memory */
+ ret = probe_kernel_read(trampoline, (void *)start_offset_caller, caller_size);
+ if (WARN_ON(ret < 0))
+ goto free;
+
+ /*
+ * Copy ftrace_common to the trampoline memory
+ * below ftrace_caller/ftrace_regs_caller. so
+ * we can merge the two function to one function.
+ */
+ ret = probe_kernel_read(trampoline + caller_size, (void *)start_offset_common, common_size);
+ if (WARN_ON(ret < 0))
+ goto free;
+
+ /*
+ * We merge the two functions to one function, so these is
+ * no need to use jump instructions to ftrace_common, modify
+ * it to NOP.
+ */
+ ip = (unsigned long)trampoline + caller_size - AARCH64_INSN_SIZE;
+ nop = aarch64_insn_gen_nop();
+ memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
+
+ /*
+ * Stored ftrace_ops at the end of the trampoline.
+ * This will be used to load the third parameter for the callback.
+ * Basically, that location at the end of the trampoline takes the
+ * place of the global function_trace_op variable.
+ */
+ ptr = (unsigned long *)(trampoline + size);
+ *ptr = (unsigned long)ops;
+
+ /*
+ * Update the trampoline ops REF
+ *
+ * OLD INSNS : ldr_l x2, function_trace_op
+ * adrp x2, sym
+ * ldr x2, [x2, :lo12:\sym]
+ *
+ * NEW INSNS:
+ * nop
+ * ldr x2, <ftrace_ops>
+ */
+ op_offset -= start_offset_common;
+ ip = (unsigned long)trampoline + caller_size + op_offset;
+ nop = aarch64_insn_gen_nop();
+ memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
+
+ op_offset += AARCH64_INSN_SIZE;
+ ip = (unsigned long)trampoline + caller_size + op_offset;
+ offset = (unsigned long)ptr - ip;
+ if (WARN_ON(offset % AARCH64_INSN_SIZE != 0))
+ goto free;
+ offset = offset / AARCH64_INSN_SIZE;
+ pc_ldr |= (offset & mask) << shift;
+ memcpy((void *)ip, &pc_ldr, AARCH64_INSN_SIZE);
+
+ ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
+
+ set_vm_flush_reset_perms(trampoline);
+
+ /*
+ * Module allocation needs to be completed by making the page
+ * executable. The page is still writable, which is a security hazard,
+ * but anyhow ftrace breaks W^X completely.
+ */
+ set_memory_x((unsigned long)trampoline, npages);
+
+ return (unsigned long)trampoline;
+
+free:
+ tramp_free(trampoline);
+ return 0;
+}
+
+static unsigned long calc_trampoline_call_offset(struct ftrace_ops *ops)
+{
+ unsigned call_offset, end_offset, offset;
+
+ call_offset = (unsigned long)&ftrace_call;
+ end_offset = (unsigned long)ftrace_common_end;
+ offset = end_offset - call_offset;
+
+ return ops->trampoline_size - AARCH64_INSN_SIZE - sizeof(void *) - offset;
+}
+
+static int ftrace_trampoline_modify_call(struct ftrace_ops *ops)
+{
+ unsigned long offset;
+ unsigned long pc;
+ ftrace_func_t func;
+ u32 new;
+
+ offset = calc_trampoline_call_offset(ops);
+ pc = ops->trampoline + offset;
+
+ func = ftrace_ops_get_func(ops);
+ new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, AARCH64_INSN_BRANCH_LINK);
+
+ return ftrace_modify_code(pc, 0, new, false);
+}
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+static unsigned long calc_trampoline_graph_call_offset(struct ftrace_ops *ops)
+{
+ unsigned end_offset, call_offset, offset;
+
+ call_offset = (unsigned long)&ftrace_graph_call;
+ end_offset = (unsigned long)ftrace_common_end;
+ offset = end_offset - call_offset;
+
+ return ops->trampoline_size - AARCH64_INSN_SIZE - sizeof(void *) - offset;
+}
+
+extern int ftrace_graph_active;
+static int ftrace_trampoline_modify_graph_call(struct ftrace_ops *ops)
+{
+ unsigned long offset;
+ unsigned long pc;
+ u32 branch, nop;
+
+ offset = calc_trampoline_graph_call_offset(ops);
+ pc = ops->trampoline + offset;
+
+ branch = aarch64_insn_gen_branch_imm(pc,
+ (unsigned long)ftrace_graph_caller,
+ AARCH64_INSN_BRANCH_NOLINK);
+ nop = aarch64_insn_gen_nop();
+
+ if (ftrace_graph_active)
+ return ftrace_modify_code(pc, 0, branch, false);
+ else
+ return ftrace_modify_code(pc, 0, nop, false);
+}
+#else
+static inline int ftrace_trampoline_modify_graph_call(struct ftrace_ops *ops)
+{
+ return 0;
+}
+#endif
+
+void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
+{
+ int npages;
+
+ if (ops->trampoline) {
+ /*
+ * The ftrace_ops caller may set up its own trampoline.
+ * In such a case, this code must not modify it.
+ */
+ if (!(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
+ return;
+ npages = PAGE_ALIGN(ops->trampoline_size) >> PAGE_SHIFT;
+ set_memory_rw(ops->trampoline, npages);
+ } else {
+ unsigned int size;
+
+ ops->trampoline = create_trampoline(ops, &size);
+ if (!ops->trampoline)
+ return;
+ ops->trampoline_size = size;
+ npages = PAGE_ALIGN(size) >> PAGE_SHIFT;
+ }
+
+ /* atomic modify trampoline: <call func> */
+ WARN_ON(ftrace_trampoline_modify_call(ops));
+
+ /* atomic modify trampoline: <call graph func> */
+ WARN_ON(ftrace_trampoline_modify_graph_call(ops));
+
+ set_memory_ro(ops->trampoline, npages);
+}
+
+static void *addr_from_call(void *ptr)
+{
+ u32 insn;
+ unsigned long offset;
+
+ if (aarch64_insn_read(ptr, &insn))
+ return NULL;
+
+ /* Make sure this is a call */
+ if (!aarch64_insn_is_bl(insn)) {
+ pr_warn("Expected bl instruction, but not\n");
+ return NULL;
+ }
+
+ offset = aarch64_get_branch_offset(insn);
+
+ return (void *)ptr + AARCH64_INSN_SIZE + offset;
+}
+
+void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
+ unsigned long frame_pointer);
+
+void *arch_ftrace_trampoline_func(struct ftrace_ops *ops, struct dyn_ftrace *rec)
+{
+ unsigned long offset;
+
+ /* If we didn't allocate this trampoline, consider it static */
+ if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
+ return NULL;
+
+ offset = calc_trampoline_call_offset(ops);
+
+ return addr_from_call((void *)ops->trampoline + offset);
+}
+
+void arch_ftrace_trampoline_free(struct ftrace_ops *ops)
+{
+ if (!ops || !(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
+ return;
+
+ tramp_free((void *)ops->trampoline);
+ ops->trampoline = 0;
+ ops->trampoline_size = 0;
+}
+#endif
+
/*
* Replace tracer function in ftrace_caller()
*/
--
2.17.1
On Thu, Jan 09, 2020 at 02:27:36PM +0000, Cheng Jian wrote:
> When we tracing multiple functions, it has to use a list
> function and cause all the other functions being traced
> to check the hash of the ftrace_ops. But this is very
> inefficient.
Just how bad is this, and when/where does it matter?
How much does this patch improve matters?
> we can call a dynamically allocated trampoline which calls
> the callback directly to solve this problem. This patch
> introduce dynamically alloced trampolines for ARM64.
>
> If a callback is registered to a function and there's no
> other callback registered to that function, the ftrace_ops
> will get its own trampoline allocated for it that will call
> the function directly.
>
> We merge two functions (ftrace_caller/ftrace_regs_caller and
> ftrace_common) into one function, so we no longer need a jump
> to ftrace_common and fix it to NOP.
>
> similar to X86_64, save the local ftrace_ops at the end.
>
> the ftrace trampoline layout :
>
> low
> ftrace_(regs_)caller => +---------------+
> | ftrace_caller |
> ftrace_common => +---------------+
> | ftrace_common |
> function_trace_op_ptr => | ... | ldr x2, <ftrace_ops>
> | | b ftrace_stub |
> | | nop | fgraph call
> | +---------------+
> +------------>| ftrace_ops |
> +---------------+
> | PLT entrys | (TODO)
> +---------------+
> high
>
> Known issues :
> If kaslr is enabled, the address of tramp and ftrace call
> may be far away. Therefore, long jump support is required.
> Here I intend to use the same solution as module relocating,
> Reserve enough space for PLT at the end when allocating, can
> use PLT to complete these long jumps.
This can happen both ways; the callsite can also be too far from the
trampoline to be able to branch to it.
I've had issues with that for other reasons, and I think that we might
be able to use -fpatchable-function-entry=N,M to place a PLT immediately
before each function for that. However, I'm wary of doing so because it
makes it much harder to modify the patch site itself.
>
> Signed-off-by: Cheng Jian <[email protected]>
> ---
> arch/arm64/kernel/entry-ftrace.S | 4 +
> arch/arm64/kernel/ftrace.c | 310 +++++++++++++++++++++++++++++++
> 2 files changed, 314 insertions(+)
>
> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
> index 7d02f9966d34..f5ee797804ac 100644
> --- a/arch/arm64/kernel/entry-ftrace.S
> +++ b/arch/arm64/kernel/entry-ftrace.S
> @@ -77,17 +77,20 @@
>
> ENTRY(ftrace_regs_caller)
> ftrace_regs_entry 1
> +GLOBAL(ftrace_regs_caller_end)
> b ftrace_common
> ENDPROC(ftrace_regs_caller)
>
> ENTRY(ftrace_caller)
> ftrace_regs_entry 0
> +GLOBAL(ftrace_caller_end)
> b ftrace_common
> ENDPROC(ftrace_caller)
>
> ENTRY(ftrace_common)
> sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
> mov x1, x9 // parent_ip (callsite's LR)
> +GLOBAL(function_trace_op_ptr)
> ldr_l x2, function_trace_op // op
> mov x3, sp // regs
>
> @@ -121,6 +124,7 @@ ftrace_common_return:
> /* Restore the callsite's SP */
> add sp, sp, #S_FRAME_SIZE + 16
>
> +GLOBAL(ftrace_common_end)
> ret x9
This doesn't look right. Surely you want the RET, too?
> ENDPROC(ftrace_common)
>
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index 8618faa82e6d..95ea68ef6228 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -10,11 +10,13 @@
> #include <linux/module.h>
> #include <linux/swab.h>
> #include <linux/uaccess.h>
> +#include <linux/vmalloc.h>
>
> #include <asm/cacheflush.h>
> #include <asm/debug-monitors.h>
> #include <asm/ftrace.h>
> #include <asm/insn.h>
> +#include <asm/set_memory.h>
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> /*
> @@ -47,6 +49,314 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
> return 0;
> }
>
> +/* ftrace dynamic trampolines */
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +#ifdef CONFIG_MODULES
> +#include <linux/moduleloader.h>
> +
> +static inline void *alloc_tramp(unsigned long size)
> +{
> + return module_alloc(size);
> +}
> +
> +static inline void tramp_free(void *tramp)
> +{
> + module_memfree(tramp);
> +}
> +#else
> +static inline void *alloc_tramp(unsigned long size)
> +{
> + return NULL;
> +}
> +
> +static inline void tramp_free(void *tramp) {}
> +#endif
> +
> +extern void ftrace_regs_caller_end(void);
> +extern void ftrace_caller_end(void);
> +extern void ftrace_common(void);
> +extern void ftrace_common_end(void);
> +
> +extern void function_trace_op_ptr(void);
> +
> +extern struct ftrace_ops *function_trace_op;
> +
> +/*
> + * ftrace_caller() or ftrace_regs_caller() trampoline
> + * +-----------------------+
> + * ftrace_(regs_)caller => | ...... |
> + * ftrace_(regs_)caller_end => | b ftrace_common | => nop
> + * +-----------------------+
> + * ftrace_common => | ...... |
> + * function_trace_op_ptr => | adrp x2, sym | => nop
> + * | ldr x2,[x2,:lo12:sym]| => ldr x2 <ftrace_op>
> + * | ...... |
> + * ftrace_common_end => | retq |
Copy-paste from x86? arm64 doesn't have a retq instruction.
> + * +-----------------------+
> + * ftrace_opt => | ftrace_opt |
> + * +-----------------------+
Typo: s/opt/ops/ ?
> + */
> +static unsigned long create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
> +{
> + unsigned long start_offset_caller, end_offset_caller, caller_size;
> + unsigned long start_offset_common, end_offset_common, common_size;
> + unsigned long op_offset, offset, size, ip, npages;
> + void *trampoline;
> + unsigned long *ptr;
> + /* ldr x2, <label> */
> + u32 pc_ldr = 0x58000002;
> + u32 mask = BIT(19) - 1;
Instead of open-coding this, please teach the insn framework how to
encode LDR (immediate).
> + int shift = 5;
> + int ret;
> + u32 nop;
> +
> + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
> + start_offset_caller = (unsigned long)ftrace_regs_caller;
> + end_offset_caller = (unsigned long)ftrace_regs_caller_end;
> + } else {
> + start_offset_caller = (unsigned long)ftrace_caller;
> + end_offset_caller = (unsigned long)ftrace_caller_end;
> + }
> + start_offset_common = (unsigned long)ftrace_common;
> + end_offset_common = (unsigned long)ftrace_common_end;
> +
> + op_offset = (unsigned long)function_trace_op_ptr;
> +
> + /*
> + * Merge ftrace_caller/ftrace_regs_caller and ftrace_common
> + * to one function in ftrace trampoline.
> + */
> + caller_size = end_offset_caller - start_offset_caller + AARCH64_INSN_SIZE;
> + common_size = end_offset_common - start_offset_common + AARCH64_INSN_SIZE;
> + size = caller_size + common_size;
> +
> + trampoline = alloc_tramp(caller_size + common_size + sizeof(void *));
> + if (!trampoline)
> + return 0;
> +
> + *tramp_size = caller_size + common_size + sizeof(void *);
> + npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
> +
> + /* Copy ftrace_caller/ftrace_regs_caller onto the trampoline memory */
> + ret = probe_kernel_read(trampoline, (void *)start_offset_caller, caller_size);
> + if (WARN_ON(ret < 0))
> + goto free;
> +
> + /*
> + * Copy ftrace_common to the trampoline memory
> + * below ftrace_caller/ftrace_regs_caller. so
> + * we can merge the two function to one function.
> + */
> + ret = probe_kernel_read(trampoline + caller_size, (void *)start_offset_common, common_size);
> + if (WARN_ON(ret < 0))
> + goto free;
> +
> + /*
> + * We merge the two functions to one function, so these is
> + * no need to use jump instructions to ftrace_common, modify
> + * it to NOP.
> + */
> + ip = (unsigned long)trampoline + caller_size - AARCH64_INSN_SIZE;
> + nop = aarch64_insn_gen_nop();
> + memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
> +
> + /*
> + * Stored ftrace_ops at the end of the trampoline.
> + * This will be used to load the third parameter for the callback.
> + * Basically, that location at the end of the trampoline takes the
> + * place of the global function_trace_op variable.
> + */
> + ptr = (unsigned long *)(trampoline + size);
> + *ptr = (unsigned long)ops;
> +
> + /*
> + * Update the trampoline ops REF
> + *
> + * OLD INSNS : ldr_l x2, function_trace_op
> + * adrp x2, sym
> + * ldr x2, [x2, :lo12:\sym]
> + *
> + * NEW INSNS:
> + * nop
> + * ldr x2, <ftrace_ops>
> + */
> + op_offset -= start_offset_common;
> + ip = (unsigned long)trampoline + caller_size + op_offset;
> + nop = aarch64_insn_gen_nop();
> + memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
> +
> + op_offset += AARCH64_INSN_SIZE;
> + ip = (unsigned long)trampoline + caller_size + op_offset;
> + offset = (unsigned long)ptr - ip;
> + if (WARN_ON(offset % AARCH64_INSN_SIZE != 0))
> + goto free;
> + offset = offset / AARCH64_INSN_SIZE;
> + pc_ldr |= (offset & mask) << shift;
> + memcpy((void *)ip, &pc_ldr, AARCH64_INSN_SIZE);
I think it would be much better to have a separate template for the
trampoline which we don't have to patch in this way. It can even be
placed into a non-executable RO section, since the template shouldn't be
executed directly.
> +
> + ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
> +
> + set_vm_flush_reset_perms(trampoline);
> +
> + /*
> + * Module allocation needs to be completed by making the page
> + * executable. The page is still writable, which is a security hazard,
> + * but anyhow ftrace breaks W^X completely.
> + */
> + set_memory_x((unsigned long)trampoline, npages);
Why is the page still writeable? Surely you can make it RO first?
Please do not break W^X restrictions; we've tried to ensure that arm64
does the right thing by default here.
Note that arm64's ftrace_modify_code() will use a writeable alias, so it
can be used after the memory has been marked RO.
> +
> + return (unsigned long)trampoline;
> +
> +free:
> + tramp_free(trampoline);
> + return 0;
> +}
> +
> +static unsigned long calc_trampoline_call_offset(struct ftrace_ops *ops)
> +{
> + unsigned call_offset, end_offset, offset;
> +
> + call_offset = (unsigned long)&ftrace_call;
> + end_offset = (unsigned long)ftrace_common_end;
> + offset = end_offset - call_offset;
> +
> + return ops->trampoline_size - AARCH64_INSN_SIZE - sizeof(void *) - offset;
> +}
> +
> +static int ftrace_trampoline_modify_call(struct ftrace_ops *ops)
> +{
> + unsigned long offset;
> + unsigned long pc;
> + ftrace_func_t func;
> + u32 new;
> +
> + offset = calc_trampoline_call_offset(ops);
> + pc = ops->trampoline + offset;
> +
> + func = ftrace_ops_get_func(ops);
> + new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, AARCH64_INSN_BRANCH_LINK);
> +
> + return ftrace_modify_code(pc, 0, new, false);
> +}
> +
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +
> +static unsigned long calc_trampoline_graph_call_offset(struct ftrace_ops *ops)
> +{
> + unsigned end_offset, call_offset, offset;
> +
> + call_offset = (unsigned long)&ftrace_graph_call;
> + end_offset = (unsigned long)ftrace_common_end;
> + offset = end_offset - call_offset;
> +
> + return ops->trampoline_size - AARCH64_INSN_SIZE - sizeof(void *) - offset;
> +}
> +
> +extern int ftrace_graph_active;
> +static int ftrace_trampoline_modify_graph_call(struct ftrace_ops *ops)
> +{
> + unsigned long offset;
> + unsigned long pc;
> + u32 branch, nop;
> +
> + offset = calc_trampoline_graph_call_offset(ops);
> + pc = ops->trampoline + offset;
> +
> + branch = aarch64_insn_gen_branch_imm(pc,
> + (unsigned long)ftrace_graph_caller,
> + AARCH64_INSN_BRANCH_NOLINK);
> + nop = aarch64_insn_gen_nop();
> +
> + if (ftrace_graph_active)
> + return ftrace_modify_code(pc, 0, branch, false);
> + else
> + return ftrace_modify_code(pc, 0, nop, false);
> +}
It should be posbile to share the bulk of this code with the non-graph
versions.
Thanks,
Mark.
Hi, Mark
Thanks for your reply.
On 2020/1/10 0:48, Mark Rutland wrote:
> On Thu, Jan 09, 2020 at 02:27:36PM +0000, Cheng Jian wrote:
>
> Just how bad is this, and when/where does it matter?
>
> How much does this patch improve matters?
I will have a test about this.
>> Known issues :
>> If kaslr is enabled, the address of tramp and ftrace call
>> may be far away. Therefore, long jump support is required.
>> Here I intend to use the same solution as module relocating,
>> Reserve enough space for PLT at the end when allocating, can
>> use PLT to complete these long jumps.
> This can happen both ways; the callsite can also be too far from the
> trampoline to be able to branch to it.
Yes, that can happen both ways.
> I've had issues with that for other reasons, and I think that we might
> be able to use -fpatchable-function-entry=N,M to place a PLT immediately
> before each function for that. However, I'm wary of doing so because it
> makes it much harder to modify the patch site itself.
This sounds good. I have no better idea than this now.
At least try it first.
>
>>
>> +GLOBAL(ftrace_common_end)
>> ret x9
> This doesn't look right. Surely you want the RET, too?
I will fix this error, thanks.
> +/*
> + * ftrace_caller() or ftrace_regs_caller() trampoline
> + * +-----------------------+
> + * ftrace_(regs_)caller => | ...... |
> + * ftrace_(regs_)caller_end => | b ftrace_common | => nop
> + * +-----------------------+
> + * ftrace_common => | ...... |
> + * function_trace_op_ptr => | adrp x2, sym | => nop
> + * | ldr x2,[x2,:lo12:sym]| => ldr x2 <ftrace_op>
> + * | ...... |
> + * ftrace_common_end => | retq |
> Copy-paste from x86? arm64 doesn't have a retq instruction.
>
>> + * +-----------------------+
>> + * ftrace_opt => | ftrace_opt |
>> + * +-----------------------+
> Typo: s/opt/ops/ ?
Sorry for these scenes.
>> + */
>> +static unsigned long create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>> +{
>> + unsigned long start_offset_caller, end_offset_caller, caller_size;
>> + unsigned long start_offset_common, end_offset_common, common_size;
>> + unsigned long op_offset, offset, size, ip, npages;
>> + void *trampoline;
>> + unsigned long *ptr;
>> + /* ldr x2, <label> */
>> + u32 pc_ldr = 0x58000002;
>> + u32 mask = BIT(19) - 1;
> Instead of open-coding this, please teach the insn framework how to
> encode LDR (immediate).
I will, Thank you.
>
>> + int shift = 5;
>> + int ret;
>> + u32 nop;
>> +
>> + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
>> + start_offset_caller = (unsigned long)ftrace_regs_caller;
>> + end_offset_caller = (unsigned long)ftrace_regs_caller_end;
>> + } else {
>> + start_offset_caller = (unsigned long)ftrace_caller;
>> + end_offset_caller = (unsigned long)ftrace_caller_end;
>> + }
>> + start_offset_common = (unsigned long)ftrace_common;
>> + end_offset_common = (unsigned long)ftrace_common_end;
>> +
>> + op_offset = (unsigned long)function_trace_op_ptr;
>> +
>> + /*
>> + * Merge ftrace_caller/ftrace_regs_caller and ftrace_common
>> + * to one function in ftrace trampoline.
>> + */
>> + caller_size = end_offset_caller - start_offset_caller + AARCH64_INSN_SIZE;
>> + common_size = end_offset_common - start_offset_common + AARCH64_INSN_SIZE;
>> + size = caller_size + common_size;
>> +
>> + trampoline = alloc_tramp(caller_size + common_size + sizeof(void *));
>> + if (!trampoline)
>> + return 0;
>> +
>> + *tramp_size = caller_size + common_size + sizeof(void *);
>> + npages = DIV_ROUND_UP(*tramp_size, PAGE_SIZE);
>> +
>> + /* Copy ftrace_caller/ftrace_regs_caller onto the trampoline memory */
>> + ret = probe_kernel_read(trampoline, (void *)start_offset_caller, caller_size);
>> + if (WARN_ON(ret < 0))
>> + goto free;
>> +
>> + /*
>> + * Copy ftrace_common to the trampoline memory
>> + * below ftrace_caller/ftrace_regs_caller. so
>> + * we can merge the two function to one function.
>> + */
>> + ret = probe_kernel_read(trampoline + caller_size, (void *)start_offset_common, common_size);
>> + if (WARN_ON(ret < 0))
>> + goto free;
>> +
>> + /*
>> + * We merge the two functions to one function, so these is
>> + * no need to use jump instructions to ftrace_common, modify
>> + * it to NOP.
>> + */
>> + ip = (unsigned long)trampoline + caller_size - AARCH64_INSN_SIZE;
>> + nop = aarch64_insn_gen_nop();
>> + memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
>> +
>> + /*
>> + * Stored ftrace_ops at the end of the trampoline.
>> + * This will be used to load the third parameter for the callback.
>> + * Basically, that location at the end of the trampoline takes the
>> + * place of the global function_trace_op variable.
>> + */
>> + ptr = (unsigned long *)(trampoline + size);
>> + *ptr = (unsigned long)ops;
>> +
>> + /*
>> + * Update the trampoline ops REF
>> + *
>> + * OLD INSNS : ldr_l x2, function_trace_op
>> + * adrp x2, sym
>> + * ldr x2, [x2, :lo12:\sym]
>> + *
>> + * NEW INSNS:
>> + * nop
>> + * ldr x2, <ftrace_ops>
>> + */
>> + op_offset -= start_offset_common;
>> + ip = (unsigned long)trampoline + caller_size + op_offset;
>> + nop = aarch64_insn_gen_nop();
>> + memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
>> +
>> + op_offset += AARCH64_INSN_SIZE;
>> + ip = (unsigned long)trampoline + caller_size + op_offset;
>> + offset = (unsigned long)ptr - ip;
>> + if (WARN_ON(offset % AARCH64_INSN_SIZE != 0))
>> + goto free;
>> + offset = offset / AARCH64_INSN_SIZE;
>> + pc_ldr |= (offset & mask) << shift;
>> + memcpy((void *)ip, &pc_ldr, AARCH64_INSN_SIZE);
> I think it would be much better to have a separate template for the
> trampoline which we don't have to patch in this way. It can even be
> placed into a non-executable RO section, since the template shouldn't be
> executed directly.
A separate template !
This may be a good way, and I think the patching here is very HACK
too(Not very friendly).
I had thought of other ways before, similar to the method on X86_64, remove
the ftrace_common(), directly modifying ftrace_caller/ftrace_reg_caller,
We will
only need to copy the code once in this way, and these is no need to modify
call ftrace_common to NOP.
Using a trampoline template sounds great. but this also means that we
need to
maintain a template(or maybe two templates: one for caller, another for
regs_caller).
Hi, Mark, what do you think about it ?
>> +
>> + ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
>> +
>> + set_vm_flush_reset_perms(trampoline);
>> +
>> + /*
>> + * Module allocation needs to be completed by making the page
>> + * executable. The page is still writable, which is a security hazard,
>> + * but anyhow ftrace breaks W^X completely.
>> + */
>> + set_memory_x((unsigned long)trampoline, npages);
> Why is the page still writeable? Surely you can make it RO first?
>
> Please do not break W^X restrictions; we've tried to ensure that arm64
> does the right thing by default here.
>
> Note that arm64's ftrace_modify_code() will use a writeable alias, so it
> can be used after the memory has been marked RO.
YEAH, I will. arm64's ftrace_modify_code can work after the trampoline has
been marked RO.
>> +
>> + return (unsigned long)trampoline;
>> +
>> +free:
>> + tramp_free(trampoline);
>> + return 0;
>> +}
>> +
>> +static unsigned long calc_trampoline_call_offset(struct ftrace_ops *ops)
>> +{
>> + unsigned call_offset, end_offset, offset;
>> +
>> + call_offset = (unsigned long)&ftrace_call;
>> + end_offset = (unsigned long)ftrace_common_end;
>> + offset = end_offset - call_offset;
>> +
>> + return ops->trampoline_size - AARCH64_INSN_SIZE - sizeof(void *) - offset;
>> +}
>> +
>> +static int ftrace_trampoline_modify_call(struct ftrace_ops *ops)
>> +{
>> + unsigned long offset;
>> + unsigned long pc;
>> + ftrace_func_t func;
>> + u32 new;
>> +
>> + offset = calc_trampoline_call_offset(ops);
>> + pc = ops->trampoline + offset;
>> +
>> + func = ftrace_ops_get_func(ops);
>> + new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, AARCH64_INSN_BRANCH_LINK);
>> +
>> + return ftrace_modify_code(pc, 0, new, false);
>> +}
>> +
>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>> +
>> +static unsigned long calc_trampoline_graph_call_offset(struct ftrace_ops *ops)
>> +{
>> + unsigned end_offset, call_offset, offset;
>> +
>> + call_offset = (unsigned long)&ftrace_graph_call;
>> + end_offset = (unsigned long)ftrace_common_end;
>> + offset = end_offset - call_offset;
>> +
>> + return ops->trampoline_size - AARCH64_INSN_SIZE - sizeof(void *) - offset;
>> +}
>> +
>> +extern int ftrace_graph_active;
>> +static int ftrace_trampoline_modify_graph_call(struct ftrace_ops *ops)
>> +{
>> + unsigned long offset;
>> + unsigned long pc;
>> + u32 branch, nop;
>> +
>> + offset = calc_trampoline_graph_call_offset(ops);
>> + pc = ops->trampoline + offset;
>> +
>> + branch = aarch64_insn_gen_branch_imm(pc,
>> + (unsigned long)ftrace_graph_caller,
>> + AARCH64_INSN_BRANCH_NOLINK);
>> + nop = aarch64_insn_gen_nop();
>> +
>> + if (ftrace_graph_active)
>> + return ftrace_modify_code(pc, 0, branch, false);
>> + else
>> + return ftrace_modify_code(pc, 0, nop, false);
>> +}
> It should be posbile to share the bulk of this code with the non-graph
> versions.
It seems that, I will cleanup my code.
>
> Thanks,
> Mark.
>
> .
Thank you very much.
-- Cheng Jian.
On Fri, Jan 10, 2020 at 07:28:17PM +0800, chengjian (D) wrote:
> On 2020/1/10 0:48, Mark Rutland wrote:
> > On Thu, Jan 09, 2020 at 02:27:36PM +0000, Cheng Jian wrote:
> > > + /*
> > > + * Update the trampoline ops REF
> > > + *
> > > + * OLD INSNS : ldr_l x2, function_trace_op
> > > + * adrp x2, sym
> > > + * ldr x2, [x2, :lo12:\sym]
> > > + *
> > > + * NEW INSNS:
> > > + * nop
> > > + * ldr x2, <ftrace_ops>
> > > + */
> > > + op_offset -= start_offset_common;
> > > + ip = (unsigned long)trampoline + caller_size + op_offset;
> > > + nop = aarch64_insn_gen_nop();
> > > + memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
> > > +
> > > + op_offset += AARCH64_INSN_SIZE;
> > > + ip = (unsigned long)trampoline + caller_size + op_offset;
> > > + offset = (unsigned long)ptr - ip;
> > > + if (WARN_ON(offset % AARCH64_INSN_SIZE != 0))
> > > + goto free;
> > > + offset = offset / AARCH64_INSN_SIZE;
> > > + pc_ldr |= (offset & mask) << shift;
> > > + memcpy((void *)ip, &pc_ldr, AARCH64_INSN_SIZE);
> > I think it would be much better to have a separate template for the
> > trampoline which we don't have to patch in this way. It can even be
> > placed into a non-executable RO section, since the template shouldn't be
> > executed directly.
>
> A separate template !
>
> This may be a good way, and I think the patching here is very HACK too(Not
> very friendly).
>
> I had thought of other ways before, similar to the method on X86_64,
> remove the ftrace_common(), directly modifying
> ftrace_caller/ftrace_reg_caller, We will only need to copy the code
> once in this way, and these is no need to modify call ftrace_common to
> NOP.
>
> Using a trampoline template sounds great. but this also means that we
> need to aintain a template(or maybe two templates: one for caller,
> another for regs_caller).
>
> Hi, Mark, what do you think about it ?
I think that having two templates is fine. We can factor
ftrace_common_return into a macro mirroring ftrace_regs_entry, and I
suspect we can probably figure out some way to factor the common
portion.
Thanks,
Mark.
On 2020/1/10 20:12, Mark Rutland wrote:
> On Fri, Jan 10, 2020 at 07:28:17PM +0800, chengjian (D) wrote:
>> On 2020/1/10 0:48, Mark Rutland wrote:
>>> On Thu, Jan 09, 2020 at 02:27:36PM +0000, Cheng Jian wrote:
>>>> + /*
>>>> + * Update the trampoline ops REF
>>>> + *
>>>> + * OLD INSNS : ldr_l x2, function_trace_op
>>>> + * adrp x2, sym
>>>> + * ldr x2, [x2, :lo12:\sym]
>>>> + *
>>>> + * NEW INSNS:
>>>> + * nop
>>>> + * ldr x2, <ftrace_ops>
>>>> + */
>>>> + op_offset -= start_offset_common;
>>>> + ip = (unsigned long)trampoline + caller_size + op_offset;
>>>> + nop = aarch64_insn_gen_nop();
>>>> + memcpy((void *)ip, &nop, AARCH64_INSN_SIZE);
>>>> +
>>>> + op_offset += AARCH64_INSN_SIZE;
>>>> + ip = (unsigned long)trampoline + caller_size + op_offset;
>>>> + offset = (unsigned long)ptr - ip;
>>>> + if (WARN_ON(offset % AARCH64_INSN_SIZE != 0))
>>>> + goto free;
>>>> + offset = offset / AARCH64_INSN_SIZE;
>>>> + pc_ldr |= (offset & mask) << shift;
>>>> + memcpy((void *)ip, &pc_ldr, AARCH64_INSN_SIZE);
>>> I think it would be much better to have a separate template for the
>>> trampoline which we don't have to patch in this way. It can even be
>>> placed into a non-executable RO section, since the template shouldn't be
>>> executed directly.
>> A separate template !
>>
>> This may be a good way, and I think the patching here is very HACK too(Not
>> very friendly).
>>
>> I had thought of other ways before, similar to the method on X86_64,
>> remove the ftrace_common(), directly modifying
>> ftrace_caller/ftrace_reg_caller, We will only need to copy the code
>> once in this way, and these is no need to modify call ftrace_common to
>> NOP.
>>
>> Using a trampoline template sounds great. but this also means that we
>> need to aintain a template(or maybe two templates: one for caller,
>> another for regs_caller).
>>
>> Hi, Mark, what do you think about it ?
> I think that having two templates is fine. We can factor
> ftrace_common_return into a macro mirroring ftrace_regs_entry, and I
> suspect we can probably figure out some way to factor the common
> portion.
>
> Thanks,
> Mark.
>
> .
OK, I will do it.
Thank you, Mark.
--Cheng Jian