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ftrace: arm64: move from REGS to ARGS

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This commit replaces arm64's support for FTRACE_WITH_REGS with support
for FTRACE_WITH_ARGS. This removes some overhead and complexity, and
removes some latent issues with inconsistent presentation of struct
pt_regs (which can only be reliably saved/restored at exception
boundaries).

FTRACE_WITH_REGS has been supported on arm64 since commit:

  3b23e4991f ("arm64: implement ftrace with regs")

As noted in the commit message, the major reasons for implementing
FTRACE_WITH_REGS were:

(1) To make it possible to use the ftrace graph tracer with pointer
    authentication, where it's necessary to snapshot/manipulate the LR
    before it is signed by the instrumented function.

(2) To make it possible to implement LIVEPATCH in future, where we need
    to hook function entry before an instrumented function manipulates
    the stack or argument registers. Practically speaking, we need to
    preserve the argument/return registers, PC, LR, and SP.

Neither of these need a struct pt_regs, and only require the set of
registers which are live at function call/return boundaries. Our calling
convention is defined by "Procedure Call Standard for the Arm® 64-bit
Architecture (AArch64)" (AKA "AAPCS64"), which can currently be found
at:

  https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst

Per AAPCS64, all function call argument and return values are held in
the following GPRs:

* X0 - X7 : parameter / result registers
* X8      : indirect result location register
* SP      : stack pointer (AKA SP)

Additionally, ad function call boundaries, the following GPRs hold
context/return information:

* X29 : frame pointer (AKA FP)
* X30 : link register (AKA LR)

... and for ftrace we need to capture the instrumented address:

 * PC  : program counter

No other GPRs are relevant, as none of the other arguments hold
parameters or return values:

* X9  - X17 : temporaries, may be clobbered
* X18       : shadow call stack pointer (or temorary)
* X19 - X28 : callee saved

This patch implements FTRACE_WITH_ARGS for arm64, only saving/restoring
the minimal set of registers necessary. This is always sufficient to
manipulate control flow (e.g. for live-patching) or to manipulate
function arguments and return values.

This reduces the necessary stack usage from 336 bytes for pt_regs down
to 112 bytes for ftrace_regs + 32 bytes for two frame records, freeing
up 188 bytes. This could be reduced further with changes to the
unwinder.

As there is no longer a need to save different sets of registers for
different features, we no longer need distinct `ftrace_caller` and
`ftrace_regs_caller` trampolines. This allows the trampoline assembly to
be simpler, and simplifies code which previously had to handle the two
trampolines.

I've tested this with the ftrace selftests, where there are no
unexpected failures.

Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Florent Revest <revest@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-5-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2022-11-03 17:05:20 +00:00 committed by Will Deacon
parent 94d095ffa0
commit 26299b3f6b
7 changed files with 187 additions and 126 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
arch/arm64/Kconfig
View File

@ -181,8 +181,10 @@ config ARM64
select HAVE_DEBUG_KMEMLEAK
select HAVE_DMA_CONTIGUOUS
select HAVE_DYNAMIC_FTRACE
select HAVE_DYNAMIC_FTRACE_WITH_ARGS \
if $(cc-option,-fpatchable-function-entry=2)
select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
if DYNAMIC_FTRACE_WITH_REGS
if DYNAMIC_FTRACE_WITH_ARGS
select HAVE_EFFICIENT_UNALIGNED_ACCESS
select HAVE_FAST_GUP
select HAVE_FTRACE_MCOUNT_RECORD
@ -233,16 +235,16 @@ config ARM64
help
ARM 64-bit (AArch64) Linux support.
config CLANG_SUPPORTS_DYNAMIC_FTRACE_WITH_REGS
config CLANG_SUPPORTS_DYNAMIC_FTRACE_WITH_ARGS
def_bool CC_IS_CLANG
# https://github.com/ClangBuiltLinux/linux/issues/1507
depends on AS_IS_GNU || (AS_IS_LLVM && (LD_IS_LLD || LD_VERSION >= 23600))
select HAVE_DYNAMIC_FTRACE_WITH_REGS
select HAVE_DYNAMIC_FTRACE_WITH_ARGS
config GCC_SUPPORTS_DYNAMIC_FTRACE_WITH_REGS
config GCC_SUPPORTS_DYNAMIC_FTRACE_WITH_ARGS
def_bool CC_IS_GCC
depends on $(cc-option,-fpatchable-function-entry=2)
select HAVE_DYNAMIC_FTRACE_WITH_REGS
select HAVE_DYNAMIC_FTRACE_WITH_ARGS
config 64BIT
def_bool y
@ -1816,7 +1818,7 @@ config ARM64_PTR_AUTH_KERNEL
# which is only understood by binutils starting with version 2.33.1.
depends on LD_IS_LLD || LD_VERSION >= 23301 || (CC_IS_GCC && GCC_VERSION < 90100)
depends on !CC_IS_CLANG || AS_HAS_CFI_NEGATE_RA_STATE
depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_ARGS)
help
If the compiler supports the -mbranch-protection or
-msign-return-address flag (e.g. GCC 7 or later), then this option
@ -1826,7 +1828,7 @@ config ARM64_PTR_AUTH_KERNEL
disabled with minimal loss of protection.
This feature works with FUNCTION_GRAPH_TRACER option only if
DYNAMIC_FTRACE_WITH_REGS is enabled.
DYNAMIC_FTRACE_WITH_ARGS is enabled.
config CC_HAS_BRANCH_PROT_PAC_RET
# GCC 9 or later, clang 8 or later
@ -1924,7 +1926,7 @@ config ARM64_BTI_KERNEL
depends on !CC_IS_GCC
# https://github.com/llvm/llvm-project/commit/a88c722e687e6780dcd6a58718350dc76fcc4cc9
depends on !CC_IS_CLANG || CLANG_VERSION >= 120000
depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_REGS)
depends on (!FUNCTION_GRAPH_TRACER || DYNAMIC_FTRACE_WITH_ARGS)
help
Build the kernel with Branch Target Identification annotations
and enable enforcement of this for kernel code. When this option

2
arch/arm64/Makefile
View File

@ -128,7 +128,7 @@ endif
CHECKFLAGS += -D__aarch64__
ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS),y)
ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_ARGS),y)
KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
CC_FLAGS_FTRACE := -fpatchable-function-entry=2
endif

72
arch/arm64/include/asm/ftrace.h
View File

@ -23,7 +23,7 @@
*/
#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
#define ARCH_SUPPORTS_FTRACE_OPS 1
#else
#define MCOUNT_ADDR ((unsigned long)_mcount)
@ -33,8 +33,7 @@
#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE
#define FTRACE_PLT_IDX 0
#define FTRACE_REGS_PLT_IDX 1
#define NR_FTRACE_PLTS 2
#define NR_FTRACE_PLTS 1
/*
* Currently, gcc tends to save the link register after the local variables
@ -69,7 +68,7 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
* Adjust addr to point at the BL in the callsite.
* See ftrace_init_nop() for the callsite sequence.
*/
if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_ARGS))
return addr + AARCH64_INSN_SIZE;
/*
* addr is the address of the mcount call instruction.
@ -78,10 +77,71 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
return addr;
}
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
struct dyn_ftrace;
struct ftrace_ops;
struct ftrace_regs;
#define arch_ftrace_get_regs(regs) NULL
struct ftrace_regs {
/* x0 - x8 */
unsigned long regs[9];
unsigned long __unused;
unsigned long fp;
unsigned long lr;
unsigned long sp;
unsigned long pc;
};
static __always_inline unsigned long
ftrace_regs_get_instruction_pointer(const struct ftrace_regs *fregs)
{
return fregs->pc;
}
static __always_inline void
ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
unsigned long pc)
{
fregs->pc = pc;
}
static __always_inline unsigned long
ftrace_regs_get_stack_pointer(const struct ftrace_regs *fregs)
{
return fregs->sp;
}
static __always_inline unsigned long
ftrace_regs_get_argument(struct ftrace_regs *fregs, unsigned int n)
{
if (n < 8)
return fregs->regs[n];
return 0;
}
static __always_inline unsigned long
ftrace_regs_get_return_value(const struct ftrace_regs *fregs)
{
return fregs->regs[0];
}
static __always_inline void
ftrace_regs_set_return_value(struct ftrace_regs *fregs,
unsigned long ret)
{
fregs->regs[0] = ret;
}
static __always_inline void
ftrace_override_function_with_return(struct ftrace_regs *fregs)
{
fregs->pc = fregs->lr;
}
int ftrace_regs_query_register_offset(const char *name);
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
#define ftrace_init_nop ftrace_init_nop

13
arch/arm64/kernel/asm-offsets.c
View File

@ -82,6 +82,19 @@ int main(void)
DEFINE(S_STACKFRAME, offsetof(struct pt_regs, stackframe));
DEFINE(PT_REGS_SIZE, sizeof(struct pt_regs));
BLANK();
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
DEFINE(FREGS_X0, offsetof(struct ftrace_regs, regs[0]));
DEFINE(FREGS_X2, offsetof(struct ftrace_regs, regs[2]));
DEFINE(FREGS_X4, offsetof(struct ftrace_regs, regs[4]));
DEFINE(FREGS_X6, offsetof(struct ftrace_regs, regs[6]));
DEFINE(FREGS_X8, offsetof(struct ftrace_regs, regs[8]));
DEFINE(FREGS_FP, offsetof(struct ftrace_regs, fp));
DEFINE(FREGS_LR, offsetof(struct ftrace_regs, lr));
DEFINE(FREGS_SP, offsetof(struct ftrace_regs, sp));
DEFINE(FREGS_PC, offsetof(struct ftrace_regs, pc));
DEFINE(FREGS_SIZE, sizeof(struct ftrace_regs));
BLANK();
#endif
#ifdef CONFIG_COMPAT
DEFINE(COMPAT_SIGFRAME_REGS_OFFSET, offsetof(struct compat_sigframe, uc.uc_mcontext.arm_r0));
DEFINE(COMPAT_RT_SIGFRAME_REGS_OFFSET, offsetof(struct compat_rt_sigframe, sig.uc.uc_mcontext.arm_r0));

123
arch/arm64/kernel/entry-ftrace.S
View File

@ -13,83 +13,58 @@
#include <asm/ftrace.h>
#include <asm/insn.h>
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
/*
* Due to -fpatchable-function-entry=2, the compiler has placed two NOPs before
* the regular function prologue. For an enabled callsite, ftrace_init_nop() and
* ftrace_make_call() have patched those NOPs to:
*
* MOV X9, LR
* BL <entry>
*
* ... where <entry> is either ftrace_caller or ftrace_regs_caller.
* BL ftrace_caller
*
* Each instrumented function follows the AAPCS, so here x0-x8 and x18-x30 are
* live (x18 holds the Shadow Call Stack pointer), and x9-x17 are safe to
* clobber.
*
* We save the callsite's context into a pt_regs before invoking any ftrace
* callbacks. So that we can get a sensible backtrace, we create a stack record
* for the callsite and the ftrace entry assembly. This is not sufficient for
* reliable stacktrace: until we create the callsite stack record, its caller
* is missing from the LR and existing chain of frame records.
* We save the callsite's context into a struct ftrace_regs before invoking any
* ftrace callbacks. So that we can get a sensible backtrace, we create frame
* records for the callsite and the ftrace entry assembly. This is not
* sufficient for reliable stacktrace: until we create the callsite stack
* record, its caller is missing from the LR and existing chain of frame
* records.
*/
.macro ftrace_regs_entry, allregs=0
/* Make room for pt_regs, plus a callee frame */
sub sp, sp, #(PT_REGS_SIZE + 16)
/* Save function arguments (and x9 for simplicity) */
stp x0, x1, [sp, #S_X0]
stp x2, x3, [sp, #S_X2]
stp x4, x5, [sp, #S_X4]
stp x6, x7, [sp, #S_X6]
stp x8, x9, [sp, #S_X8]
/* Optionally save the callee-saved registers, always save the FP */
.if \allregs == 1
stp x10, x11, [sp, #S_X10]
stp x12, x13, [sp, #S_X12]
stp x14, x15, [sp, #S_X14]
stp x16, x17, [sp, #S_X16]
stp x18, x19, [sp, #S_X18]
stp x20, x21, [sp, #S_X20]
stp x22, x23, [sp, #S_X22]
stp x24, x25, [sp, #S_X24]
stp x26, x27, [sp, #S_X26]
stp x28, x29, [sp, #S_X28]
.else
str x29, [sp, #S_FP]
.endif
/* Save the callsite's SP and LR */
add x10, sp, #(PT_REGS_SIZE + 16)
stp x9, x10, [sp, #S_LR]
/* Save the PC after the ftrace callsite */
str x30, [sp, #S_PC]
/* Create a frame record for the callsite above pt_regs */
stp x29, x9, [sp, #PT_REGS_SIZE]
add x29, sp, #PT_REGS_SIZE
/* Create our frame record within pt_regs. */
stp x29, x30, [sp, #S_STACKFRAME]
add x29, sp, #S_STACKFRAME
.endm
SYM_CODE_START(ftrace_regs_caller)
bti c
ftrace_regs_entry 1
b ftrace_common
SYM_CODE_END(ftrace_regs_caller)
SYM_CODE_START(ftrace_caller)
bti c
ftrace_regs_entry 0
b ftrace_common
SYM_CODE_END(ftrace_caller)
SYM_CODE_START(ftrace_common)
/* Save original SP */
mov x10, sp
/* Make room for ftrace regs, plus two frame records */
sub sp, sp, #(FREGS_SIZE + 32)
/* Save function arguments */
stp x0, x1, [sp, #FREGS_X0]
stp x2, x3, [sp, #FREGS_X2]
stp x4, x5, [sp, #FREGS_X4]
stp x6, x7, [sp, #FREGS_X6]
str x8, [sp, #FREGS_X8]
/* Save the callsite's FP, LR, SP */
str x29, [sp, #FREGS_FP]
str x9, [sp, #FREGS_LR]
str x10, [sp, #FREGS_SP]
/* Save the PC after the ftrace callsite */
str x30, [sp, #FREGS_PC]
/* Create a frame record for the callsite above the ftrace regs */
stp x29, x9, [sp, #FREGS_SIZE + 16]
add x29, sp, #FREGS_SIZE + 16
/* Create our frame record above the ftrace regs */
stp x29, x30, [sp, #FREGS_SIZE]
add x29, sp, #FREGS_SIZE
sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
mov x1, x9 // parent_ip (callsite's LR)
ldr_l x2, function_trace_op // op
@ -104,24 +79,24 @@ SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
* to restore x0-x8, x29, and x30.
*/
/* Restore function arguments */
ldp x0, x1, [sp]
ldp x2, x3, [sp, #S_X2]
ldp x4, x5, [sp, #S_X4]
ldp x6, x7, [sp, #S_X6]
ldr x8, [sp, #S_X8]
ldp x0, x1, [sp, #FREGS_X0]
ldp x2, x3, [sp, #FREGS_X2]
ldp x4, x5, [sp, #FREGS_X4]
ldp x6, x7, [sp, #FREGS_X6]
ldr x8, [sp, #FREGS_X8]
/* Restore the callsite's FP, LR, PC */
ldr x29, [sp, #S_FP]
ldr x30, [sp, #S_LR]
ldr x9, [sp, #S_PC]
ldr x29, [sp, #FREGS_FP]
ldr x30, [sp, #FREGS_LR]
ldr x9, [sp, #FREGS_PC]
/* Restore the callsite's SP */
add sp, sp, #PT_REGS_SIZE + 16
add sp, sp, #FREGS_SIZE + 32
ret x9
SYM_CODE_END(ftrace_common)
SYM_CODE_END(ftrace_caller)
#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
#else /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */
/*
* Gcc with -pg will put the following code in the beginning of each function:
@ -293,7 +268,7 @@ SYM_FUNC_START(ftrace_graph_caller)
mcount_exit
SYM_FUNC_END(ftrace_graph_caller)
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */
SYM_TYPED_FUNC_START(ftrace_stub)
ret

82
arch/arm64/kernel/ftrace.c
View File

@ -17,6 +17,49 @@
#include <asm/insn.h>
#include <asm/patching.h>
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
struct fregs_offset {
const char *name;
int offset;
};
#define FREGS_OFFSET(n, field) \
{ \
.name = n, \
.offset = offsetof(struct ftrace_regs, field), \
}
static const struct fregs_offset fregs_offsets[] = {
FREGS_OFFSET("x0", regs[0]),
FREGS_OFFSET("x1", regs[1]),
FREGS_OFFSET("x2", regs[2]),
FREGS_OFFSET("x3", regs[3]),
FREGS_OFFSET("x4", regs[4]),
FREGS_OFFSET("x5", regs[5]),
FREGS_OFFSET("x6", regs[6]),
FREGS_OFFSET("x7", regs[7]),
FREGS_OFFSET("x8", regs[8]),
FREGS_OFFSET("x29", fp),
FREGS_OFFSET("x30", lr),
FREGS_OFFSET("lr", lr),
FREGS_OFFSET("sp", sp),
FREGS_OFFSET("pc", pc),
};
int ftrace_regs_query_register_offset(const char *name)
{
for (int i = 0; i < ARRAY_SIZE(fregs_offsets); i++) {
const struct fregs_offset *roff = &fregs_offsets[i];
if (!strcmp(roff->name, name))
return roff->offset;
}
return -EINVAL;
}
#endif
#ifdef CONFIG_DYNAMIC_FTRACE
/*
* Replace a single instruction, which may be a branch or NOP.
@ -70,9 +113,6 @@ static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
if (addr == FTRACE_ADDR)
return &plt[FTRACE_PLT_IDX];
if (addr == FTRACE_REGS_ADDR &&
IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
return &plt[FTRACE_REGS_PLT_IDX];
#endif
return NULL;
}
@ -154,25 +194,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
return ftrace_modify_code(pc, old, new, true);
}
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
{
unsigned long pc = rec->ip;
u32 old, new;
if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
return -EINVAL;
if (!ftrace_find_callable_addr(rec, NULL, &addr))
return -EINVAL;
old = aarch64_insn_gen_branch_imm(pc, old_addr,
AARCH64_INSN_BRANCH_LINK);
new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
return ftrace_modify_code(pc, old, new, true);
}
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
/*
* The compiler has inserted two NOPs before the regular function prologue.
* All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are live,
@ -228,7 +250,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
*
* Note: 'mod' is only set at module load time.
*/
if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) &&
if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_ARGS) &&
IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && mod) {
return aarch64_insn_patch_text_nosync((void *)pc, new);
}
@ -279,19 +301,11 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
#ifdef CONFIG_DYNAMIC_FTRACE
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op, struct ftrace_regs *fregs)
{
/*
* When DYNAMIC_FTRACE_WITH_REGS is selected, `fregs` can never be NULL
* and arch_ftrace_get_regs(fregs) will always give a non-NULL pt_regs
* in which we can safely modify the LR.
*/
struct pt_regs *regs = arch_ftrace_get_regs(fregs);
unsigned long *parent = (unsigned long *)&procedure_link_pointer(regs);
prepare_ftrace_return(ip, parent, frame_pointer(regs));
prepare_ftrace_return(ip, &fregs->lr, fregs->fp);
}
#else
/*
@ -323,6 +337,6 @@ int ftrace_disable_ftrace_graph_caller(void)
{
return ftrace_modify_graph_caller(false);
}
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

3
arch/arm64/kernel/module.c
View File

@ -497,9 +497,6 @@ static int module_init_ftrace_plt(const Elf_Ehdr *hdr,
__init_plt(&plts[FTRACE_PLT_IDX], FTRACE_ADDR);
if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
__init_plt(&plts[FTRACE_REGS_PLT_IDX], FTRACE_REGS_ADDR);
mod->arch.ftrace_trampolines = plts;
#endif
return 0;