Quoting Sami Tolvanen (2020-12-11 10:46:22)
> LLD always splits sections with LTO, which increases module sizes. This
> change adds linker script rules to merge the split sections in the final
> module.
>
> Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
This patch fixes a warning I see on arm64 devices running the 5.10 LTS kernel.
Can we queue this to the stable tree once it lands in Linus' tree?
sysfs: cannot create duplicate filename '/module/configs/sections/__patchable_function_entries'
CPU: 3 PID: 4173 Comm: modprobe Not tainted 5.10.13 #10
Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
Call trace:
dump_backtrace+0x0/0x1c0
show_stack+0x24/0x30
dump_stack+0xc0/0x120
sysfs_warn_dup+0x74/0x90
sysfs_add_file_mode_ns+0x12c/0x178
internal_create_group+0x264/0x36c
sysfs_create_group+0x24/0x30
add_sect_attrs+0x154/0x188
mod_sysfs_setup+0x208/0x284
load_module+0xff8/0x1158
__arm64_sys_finit_module+0xb4/0xf0
el0_svc_common+0xf4/0x1c0
do_el0_svc_compat+0x2c/0x40
el0_svc_compat+0x10/0x1c
el0_sync_compat_handler+0xc0/0xf0
el0_sync_compat+0x178/0x180
The problem is that the section __patchable_function_entries is present
twice in the kernel module I've compiled. I see that
__patchable_function_entries is used on arm64 now that we have commit
a1326b17ac03 ("module/ftrace: handle patchable-function-entry") combined
with commit 3b23e4991fb6 ("arm64: implement ftrace with regs").
This linker script change nicely combines the section into one instead
of two.
Before:
$ readelf -WS configs.ko
There are 29 section headers, starting at offset 0xad78:
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 0] NULL 0000000000000000 000000 000000 00 0 0 0
[ 1] .plt NOBITS 0000000000000000 000040 000001 00 AX 0 0 16
[ 2] .init.plt NOBITS 0000000000000000 000040 000001 00 AX 0 0 1
[ 3] .text.ftrace_trampoline NOBITS 0000000000000000 000040 000001 00 AX 0 0 1
[ 4] .text PROGBITS 0000000000000000 000040 00004c 00 AX 0 0 4
[ 5] .rela.text RELA 0000000000000000 00aa10 000078 18 I 26 4 8
[ 6] __patchable_function_entries PROGBITS 0000000000000000 000090 000008 00 WAL 4 0 8
[ 7] .rela__patchable_function_entries RELA 0000000000000000 00aa88 000018 18 I 26 6 8
[ 8] .rodata PROGBITS 0000000000000000 000098 009c98 00 A 0 0 8
[ 9] .rela.rodata RELA 0000000000000000 00aaa0 000030 18 I 26 8 8
[10] .init.text PROGBITS 0000000000000000 009d30 000068 00 AX 0 0 4
[11] .rela.init.text RELA 0000000000000000 00aad0 0000f0 18 I 26 10 8
[12] __patchable_function_entries PROGBITS 0000000000000000 009d98 000008 00 WAL 10 0 8
[13] .rela__patchable_function_entries RELA 0000000000000000 00abc0 000018 18 I 26 12 8
[14] .exit.text PROGBITS 0000000000000000 009da0 000028 00 AX 0 0 4
[15] .rela.exit.text RELA 0000000000000000 00abd8 000048 18 I 26 14 8
[16] .modinfo PROGBITS 0000000000000000 009dc8 0000b1 00 A 0 0 1
[17] .rodata.str1.1 PROGBITS 0000000000000000 009e79 00000a 01 AMS 0 0 1
[18] .comment PROGBITS 0000000000000000 009e83 0000ce 01 MS 0 0 1
[19] .note.Linux NOTE 0000000000000000 009f54 000018 00 A 0 0 4
[20] .gnu.linkonce.this_module PROGBITS 0000000000000000 009f80 000380 00 WA 0 0 64
[21] .rela.gnu.linkonce.this_module RELA 0000000000000000 00ac20 000030 18 I 26 20 8
[22] .note.gnu.build-id NOTE 0000000000000000 00a300 000024 00 A 0 0 4
[23] .note.gnu.property NOTE 0000000000000000 00a328 000020 00 A 0 0 8
[24] .note.GNU-stack PROGBITS 0000000000000000 00a348 000000 00 0 0 1
[25] .gnu_debuglink PROGBITS 0000000000000000 00a348 000018 00 0 0 4
[26] .symtab SYMTAB 0000000000000000 00a360 0004f8 18 27 43 8
[27] .strtab STRTAB 0000000000000000 00a858 0001b1 00 0 0 1
[28] .shstrtab STRTAB 0000000000000000 00ac50 000128 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
p (processor specific)
After:
$ readelf -WS configs.ko
There are 26 section headers, starting at offset 0xad40:
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 0] NULL 0000000000000000 000000 000000 00 0 0 0
[ 1] __patchable_function_entries PROGBITS 0000000000000000 000040 000010 00 WAL 5 0 8
[ 2] .rela__patchable_function_entries RELA 0000000000000000 00a9e0 000030 18 I 23 1 8
[ 3] .rodata PROGBITS 0000000000000000 000050 009ca2 00 AMS 0 0 8
[ 4] .rela.rodata RELA 0000000000000000 00aa10 000030 18 I 23 3 8
[ 5] .text PROGBITS 0000000000000000 009cf4 00004c 00 AX 0 0 4
[ 6] .rela.text RELA 0000000000000000 00aa40 000078 18 I 23 5 8
[ 7] .plt NOBITS 0000000000000000 009d40 000001 00 AX 0 0 16
[ 8] .init.plt NOBITS 0000000000000000 009d40 000001 00 AX 0 0 1
[ 9] .text.ftrace_trampoline NOBITS 0000000000000000 009d40 000001 00 AX 0 0 1
[10] .init.text PROGBITS 0000000000000000 009d40 000068 00 AX 0 0 4
[11] .rela.init.text RELA 0000000000000000 00aab8 0000f0 18 I 23 10 8
[12] .exit.text PROGBITS 0000000000000000 009da8 000028 00 AX 0 0 4
[13] .rela.exit.text RELA 0000000000000000 00aba8 000048 18 I 23 12 8
[14] .modinfo PROGBITS 0000000000000000 009dd0 0000b1 00 A 0 0 1
[15] .comment PROGBITS 0000000000000000 009e81 0000ce 01 MS 0 0 1
[16] .note.Linux NOTE 0000000000000000 009f50 000018 00 A 0 0 4
[17] .gnu.linkonce.this_module PROGBITS 0000000000000000 009f80 000380 00 WA 0 0 64
[18] .rela.gnu.linkonce.this_module RELA 0000000000000000 00abf0 000030 18 I 23 17 8
[19] .note.gnu.build-id NOTE 0000000000000000 00a300 000024 00 A 0 0 4
[20] .note.gnu.property NOTE 0000000000000000 00a328 000020 00 A 0 0 8
[21] .note.GNU-stack PROGBITS 0000000000000000 00a348 000000 00 0 0 1
[22] .gnu_debuglink PROGBITS 0000000000000000 00a348 000018 00 0 0 4
[23] .symtab SYMTAB 0000000000000000 00a360 0004c8 18 24 41 8
[24] .strtab STRTAB 0000000000000000 00a828 0001b1 00 0 0 1
[25] .shstrtab STRTAB 0000000000000000 00ac20 000119 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
p (processor specific)
> scripts/module.lds.S | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/scripts/module.lds.S b/scripts/module.lds.S
> index 69b9b71a6a47..18d5b8423635 100644
> --- a/scripts/module.lds.S
> +++ b/scripts/module.lds.S
> @@ -23,6 +23,30 @@ SECTIONS {
> .init_array 0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) }
>
> __jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) }
> +
> + __patchable_function_entries : { *(__patchable_function_entries) }
> +
> + /*
> + * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and
> + * -ffunction-sections, which increases the size of the final module.
> + * Merge the split sections in the final binary.
> + */
> + .bss : {
> + *(.bss .bss.[0-9a-zA-Z_]*)
> + *(.bss..L*)
> + }
> +
> + .data : {
> + *(.data .data.[0-9a-zA-Z_]*)
> + *(.data..L*)
> + }
> +
> + .rodata : {
> + *(.rodata .rodata.[0-9a-zA-Z_]*)
> + *(.rodata..L*)
> + }
> +
> + .text : { *(.text .text.[0-9a-zA-Z_]*) }
> }
>
