| Message ID | 20250303065345.229298-4-dongml2@chinatelecom.cn (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | per-function storage support | expand |
On Mon, 3 Mar 2025 14:53:44 +0800 Menglong Dong <menglong8.dong@gmail.com> wrote: > In the third case, we make the kernel function 32 bytes aligned, and there > will be 32 bytes padding before the functions. According to my testing, > the text size didn't increase on this case, which is weird. > > With 16-bytes padding: > > -rwxr-xr-x 1 401190688 x86-dev/vmlinux* > -rw-r--r-- 1 251068 x86-dev/vmlinux.a > -rw-r--r-- 1 851892992 x86-dev/vmlinux.o > -rw-r--r-- 1 12395008 x86-dev/arch/x86/boot/bzImage > > With 32-bytes padding: > > -rwxr-xr-x 1 401318128 x86-dev/vmlinux* > -rw-r--r-- 1 251154 x86-dev/vmlinux.a > -rw-r--r-- 1 853636704 x86-dev/vmlinux.o > -rw-r--r-- 1 12509696 x86-dev/arch/x86/boot/bzImage Use the "size" command to see the differences in sizes and not the file size. $ size vmlinux text data bss dec hex filename 36892658 9798658 16982016 63673332 3cb93f4 vmlinux -- Steve
On Tue, Mar 4, 2025 at 12:05 AM Steven Rostedt <rostedt@goodmis.org> wrote: > > On Mon, 3 Mar 2025 14:53:44 +0800 > Menglong Dong <menglong8.dong@gmail.com> wrote: > > > In the third case, we make the kernel function 32 bytes aligned, and there > > will be 32 bytes padding before the functions. According to my testing, > > the text size didn't increase on this case, which is weird. > > > > With 16-bytes padding: > > > > -rwxr-xr-x 1 401190688 x86-dev/vmlinux* > > -rw-r--r-- 1 251068 x86-dev/vmlinux.a > > -rw-r--r-- 1 851892992 x86-dev/vmlinux.o > > -rw-r--r-- 1 12395008 x86-dev/arch/x86/boot/bzImage > > > > With 32-bytes padding: > > > > -rwxr-xr-x 1 401318128 x86-dev/vmlinux* > > -rw-r--r-- 1 251154 x86-dev/vmlinux.a > > -rw-r--r-- 1 853636704 x86-dev/vmlinux.o > > -rw-r--r-- 1 12509696 x86-dev/arch/x86/boot/bzImage > > Use the "size" command to see the differences in sizes and not the file size. > > $ size vmlinux > text data bss dec hex filename > 36892658 9798658 16982016 63673332 3cb93f4 vmlinux Great! It seems that the way I tested has something wrong. I'll compare the text size with "size" command later. Thanks! Menglong Dong > > -- Steve
On Tue, Mar 4, 2025 at 10:07 AM Menglong Dong <menglong8.dong@gmail.com> wrote: > > On Tue, Mar 4, 2025 at 12:05 AM Steven Rostedt <rostedt@goodmis.org> wrote: > > > > On Mon, 3 Mar 2025 14:53:44 +0800 > > Menglong Dong <menglong8.dong@gmail.com> wrote: > > > > > In the third case, we make the kernel function 32 bytes aligned, and there > > > will be 32 bytes padding before the functions. According to my testing, > > > the text size didn't increase on this case, which is weird. > > > > > > With 16-bytes padding: > > > > > > -rwxr-xr-x 1 401190688 x86-dev/vmlinux* > > > -rw-r--r-- 1 251068 x86-dev/vmlinux.a > > > -rw-r--r-- 1 851892992 x86-dev/vmlinux.o > > > -rw-r--r-- 1 12395008 x86-dev/arch/x86/boot/bzImage > > > > > > With 32-bytes padding: > > > > > > -rwxr-xr-x 1 401318128 x86-dev/vmlinux* > > > -rw-r--r-- 1 251154 x86-dev/vmlinux.a > > > -rw-r--r-- 1 853636704 x86-dev/vmlinux.o > > > -rw-r--r-- 1 12509696 x86-dev/arch/x86/boot/bzImage > > > > Use the "size" command to see the differences in sizes and not the file size. > > > > $ size vmlinux > > text data bss dec hex filename > > 36892658 9798658 16982016 63673332 3cb93f4 vmlinux > > Great! It seems that the way I tested has something wrong. I'll > compare the text size with "size" command later. With the size command, the text size with 32-bytes padding is: text data bss dec hex filename 48299471 14776173 18345936 81421580 4da650c x86-dev/vmlinux And with 16-bytes padding is: text data bss dec hex filename 46620640 14772017 18458396 79851053 4c26e2d x86-dev/vmlinux It increases about 3%, which I think is acceptable in this case. I'll post the message in the commit log of the next version. Thanks! Menglong Dong > > Thanks! > Menglong Dong > > > > > -- Steve
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index be2c311f5118..fe5a98401135 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2509,6 +2509,24 @@ config PREFIX_SYMBOLS def_bool y depends on CALL_PADDING && !CFI_CLANG +config FUNCTION_METADATA + bool "Per-function metadata storage support" + default y + depends on CC_HAS_ENTRY_PADDING && OBJTOOL + select CALL_PADDING + select FUNCTION_ALIGNMENT_32B if ((CFI_CLANG && CALL_THUNKS) || FINEIBT) + help + Support per-function metadata storage for kernel functions, and + get the metadata of the function by its address with almost no + overhead. + + The index of the metadata will be stored in the function padding + and consumes 5-bytes. FUNCTION_ALIGNMENT_32B will be selected if + "(CFI_CLANG && CALL_THUNKS) || FINEIBT" to make sure there is + enough available padding space for this function. However, it + seems that the text size almost don't change, compare with + FUNCTION_ALIGNMENT_16B. + menuconfig CPU_MITIGATIONS bool "Mitigations for CPU vulnerabilities" default y diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h index f9cb4d07df58..d5cbb8e18fd7 100644 --- a/arch/x86/include/asm/ftrace.h +++ b/arch/x86/include/asm/ftrace.h @@ -4,6 +4,28 @@ #include <asm/ptrace.h> +#ifdef CONFIG_FUNCTION_METADATA +#if (defined(CONFIG_CFI_CLANG) && defined(CONFIG_CALL_THUNKS)) || (defined(CONFIG_FINEIBT)) + /* the CONFIG_FUNCTION_PADDING_BYTES is 32 in this case, use the + * range: [align + 8, align + 13]. + */ + #define KFUNC_MD_INSN_OFFSET (CONFIG_FUNCTION_PADDING_BYTES - 8) + #define KFUNC_MD_DATA_OFFSET (CONFIG_FUNCTION_PADDING_BYTES - 9) +#else + #ifdef CONFIG_CFI_CLANG + /* use the space that CALL_THUNKS suppose to use */ + #define KFUNC_MD_INSN_OFFSET (5) + #define KFUNC_MD_DATA_OFFSET (4) + #else + /* use the space that CFI_CLANG suppose to use */ + #define KFUNC_MD_INSN_OFFSET (CONFIG_FUNCTION_PADDING_BYTES) + #define KFUNC_MD_DATA_OFFSET (CONFIG_FUNCTION_PADDING_BYTES - 1) + #endif +#endif + +#define KFUNC_MD_INSN_SIZE (5) +#endif + #ifdef CONFIG_FUNCTION_TRACER #ifndef CC_USING_FENTRY # error Compiler does not support fentry? @@ -168,4 +190,36 @@ static inline bool arch_trace_is_compat_syscall(struct pt_regs *regs) #endif /* !COMPILE_OFFSETS */ #endif /* !__ASSEMBLY__ */ +#if !defined(__ASSEMBLY__) && defined(CONFIG_FUNCTION_METADATA) +#include <asm/text-patching.h> + +static inline bool kfunc_md_arch_exist(void *ip) +{ + return *(u8 *)(ip - KFUNC_MD_INSN_OFFSET) == 0xB8; +} + +static inline void kfunc_md_arch_pretend(u8 *insn, u32 index) +{ + *insn = 0xB8; + *(u32 *)(insn + 1) = index; +} + +static inline void kfunc_md_arch_nops(u8 *insn) +{ + *(insn++) = BYTES_NOP1; + *(insn++) = BYTES_NOP1; + *(insn++) = BYTES_NOP1; + *(insn++) = BYTES_NOP1; + *(insn++) = BYTES_NOP1; +} + +static inline int kfunc_md_arch_poke(void *ip, u8 *insn) +{ + text_poke(ip, insn, KFUNC_MD_INSN_SIZE); + text_poke_sync(); + return 0; +} + +#endif + #endif /* _ASM_X86_FTRACE_H */
With CONFIG_CALL_PADDING enabled, there will be 16-bytes padding space before all the kernel functions. And some kernel features can use it, such as MITIGATION_CALL_DEPTH_TRACKING, CFI_CLANG, FINEIBT, etc. In my research, MITIGATION_CALL_DEPTH_TRACKING will consume the tail 9-bytes in the function padding, CFI_CLANG will consume the head 5-bytes, and FINEIBT will consume all the 16 bytes if it is enabled. So there will be no space for us if MITIGATION_CALL_DEPTH_TRACKING and CFI_CLANG are both enabled, or FINEIBT is enabled. In x86, we need 5-bytes to prepend a "mov %eax xxx" insn, which can hold a 4-bytes index. So we have following logic: 1. use the head 5-bytes if CFI_CLANG is not enabled 2. use the tail 5-bytes if MITIGATION_CALL_DEPTH_TRACKING and FINEIBT are not enabled 3. compile the kernel with FUNCTION_ALIGNMENT_32B otherwise In the third case, we make the kernel function 32 bytes aligned, and there will be 32 bytes padding before the functions. According to my testing, the text size didn't increase on this case, which is weird. With 16-bytes padding: -rwxr-xr-x 1 401190688 x86-dev/vmlinux* -rw-r--r-- 1 251068 x86-dev/vmlinux.a -rw-r--r-- 1 851892992 x86-dev/vmlinux.o -rw-r--r-- 1 12395008 x86-dev/arch/x86/boot/bzImage With 32-bytes padding: -rwxr-xr-x 1 401318128 x86-dev/vmlinux* -rw-r--r-- 1 251154 x86-dev/vmlinux.a -rw-r--r-- 1 853636704 x86-dev/vmlinux.o -rw-r--r-- 1 12509696 x86-dev/arch/x86/boot/bzImage The way I tested should be right, and this is a good news for us. On the third case, the layout of the padding space will be like this if fineibt is enabled: __cfi_func: mov -- 5 -- cfi, not used anymore nop nop nop mov -- 5 -- function metadata nop nop nop fineibt -- 16 -- fineibt func: nopw -- 4 ...... I tested the fineibt with "cfi=fineibt" cmdline, and it works well together with FUNCTION_METADATA enabled. And I also tested the performance of this function by setting metadata for all the kernel function, and it consumes 0.7s for 70k+ functions, not bad :/ I can't find a machine that support IBT, so I didn't test the IBT. I'd appreciate it if someone can do this testing for me :/ Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn> --- v3: - select FUNCTION_ALIGNMENT_32B on case3, instead of extra 5-bytes --- arch/x86/Kconfig | 18 ++++++++++++ arch/x86/include/asm/ftrace.h | 54 +++++++++++++++++++++++++++++++++++ 2 files changed, 72 insertions(+)