[v3,05/13] aarch64: Add BTI support to assembly files
Commit Message
From: Sudakshina Das <sudi.das@arm.com>
To enable building glibc with branch protection, assembly code
needs BTI landing pads and ELF object file markings in the form
of a GNU property note.
The landing pads are unconditionally added to all functions that
may be indirectly called. When the code segment is not mapped
with PROT_BTI these instructions are nops. They are kept in the
code when BTI is not supported so that the layout of performance
critical code is unchanged across configurations.
The GNU property notes are only added when there is support for
BTI in the toolchain, because old binutils does not handle the
notes right. (Does not know how to merge them nor to put them in
PT_GNU_PROPERTY segment instead of PT_NOTE, and some versions
of binutils emit warnings about the unknown GNU property. In
such cases the produced libc binaries would not have valid
ELF marking so BTI would not be enabled.)
Note: functions using ENTRY or ENTRY_ALIGN now start with an
additional BTI c, so alignment of the following code changes,
but ENTRY_ALIGN_AND_PAD was fixed so there is no change to the
existing code layout. Some string functions may need to be
tuned for optimal performance after this commit.
Co-authored-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
---
sysdeps/aarch64/crti.S | 2 ++
sysdeps/aarch64/crtn.S | 2 ++
sysdeps/aarch64/dl-tlsdesc.S | 3 +++
sysdeps/aarch64/dl-trampoline.S | 2 ++
sysdeps/aarch64/start.S | 1 +
sysdeps/aarch64/sysdep.h | 34 ++++++++++++++++++++++++++++++++-
6 files changed, 43 insertions(+), 1 deletion(-)
Comments
On 15/05/2020 11:40, Szabolcs Nagy wrote:
> From: Sudakshina Das <sudi.das@arm.com>
>
> To enable building glibc with branch protection, assembly code
> needs BTI landing pads and ELF object file markings in the form
> of a GNU property note.
>
> The landing pads are unconditionally added to all functions that
> may be indirectly called. When the code segment is not mapped
> with PROT_BTI these instructions are nops. They are kept in the
> code when BTI is not supported so that the layout of performance
> critical code is unchanged across configurations.
>
> The GNU property notes are only added when there is support for
> BTI in the toolchain, because old binutils does not handle the
> notes right. (Does not know how to merge them nor to put them in
> PT_GNU_PROPERTY segment instead of PT_NOTE, and some versions
> of binutils emit warnings about the unknown GNU property. In
> such cases the produced libc binaries would not have valid
> ELF marking so BTI would not be enabled.)
>
> Note: functions using ENTRY or ENTRY_ALIGN now start with an
> additional BTI c, so alignment of the following code changes,
> but ENTRY_ALIGN_AND_PAD was fixed so there is no change to the
> existing code layout. Some string functions may need to be
> tuned for optimal performance after this commit.
>
> Co-authored-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
LGTM with a small change with depends on previous commit change
(with I also added a comment).
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> sysdeps/aarch64/crti.S | 2 ++
> sysdeps/aarch64/crtn.S | 2 ++
> sysdeps/aarch64/dl-tlsdesc.S | 3 +++
> sysdeps/aarch64/dl-trampoline.S | 2 ++
> sysdeps/aarch64/start.S | 1 +
> sysdeps/aarch64/sysdep.h | 34 ++++++++++++++++++++++++++++++++-
> 6 files changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/sysdeps/aarch64/crti.S b/sysdeps/aarch64/crti.S
> index 1728eac37a..c346bcad72 100644
> --- a/sysdeps/aarch64/crti.S
> +++ b/sysdeps/aarch64/crti.S
> @@ -75,6 +75,7 @@ call_weak_fn:
> .hidden _init
> .type _init, %function
> _init:
> + BTI_C
> stp x29, x30, [sp, -16]!
> mov x29, sp
> #if PREINIT_FUNCTION_WEAK
> @@ -89,5 +90,6 @@ _init:
> .hidden _fini
> .type _fini, %function
> _fini:
> + BTI_C
> stp x29, x30, [sp, -16]!
> mov x29, sp
Ok.
> diff --git a/sysdeps/aarch64/crtn.S b/sysdeps/aarch64/crtn.S
> index c3e97cc449..0c1ef112c2 100644
> --- a/sysdeps/aarch64/crtn.S
> +++ b/sysdeps/aarch64/crtn.S
> @@ -37,6 +37,8 @@
> /* crtn.S puts function epilogues in the .init and .fini sections
> corresponding to the prologues in crti.S. */
>
> +#include <sysdep.h>
> +
> .section .init,"ax",%progbits
> ldp x29, x30, [sp], 16
> RET
Ok.
> diff --git a/sysdeps/aarch64/dl-tlsdesc.S b/sysdeps/aarch64/dl-tlsdesc.S
> index 557ad1d505..9d96c8632a 100644
> --- a/sysdeps/aarch64/dl-tlsdesc.S
> +++ b/sysdeps/aarch64/dl-tlsdesc.S
> @@ -74,6 +74,7 @@
> cfi_startproc
> .align 2
> _dl_tlsdesc_return:
> + BTI_C
> DELOUSE (0)
> ldr PTR_REG (0), [x0, #PTR_SIZE]
> RET
> @@ -95,6 +96,7 @@ _dl_tlsdesc_return:
> cfi_startproc
> .align 2
> _dl_tlsdesc_undefweak:
> + BTI_C
> str x1, [sp, #-16]!
> cfi_adjust_cfa_offset (16)
> DELOUSE (0)
> @@ -142,6 +144,7 @@ _dl_tlsdesc_undefweak:
> cfi_startproc
> .align 2
> _dl_tlsdesc_dynamic:
> + BTI_C
> DELOUSE (0)
>
> /* Save just enough registers to support fast path, if we fall
Ok.
> diff --git a/sysdeps/aarch64/dl-trampoline.S b/sysdeps/aarch64/dl-trampoline.S
> index 94e965c096..2cbfa81434 100644
> --- a/sysdeps/aarch64/dl-trampoline.S
> +++ b/sysdeps/aarch64/dl-trampoline.S
> @@ -35,6 +35,7 @@
> cfi_startproc
> .align 2
> _dl_runtime_resolve:
> + BTI_C
> /* AArch64 we get called with:
> ip0 &PLTGOT[2]
> ip1 temp(dl resolver entry point)
> @@ -126,6 +127,7 @@ _dl_runtime_resolve:
> cfi_startproc
> .align 2
> _dl_runtime_profile:
> + BTI_C
> /* AArch64 we get called with:
> ip0 &PLTGOT[2]
> ip1 temp(dl resolver entry point)
OK.
> diff --git a/sysdeps/aarch64/start.S b/sysdeps/aarch64/start.S
> index d96cf57e2d..75393e1c18 100644
> --- a/sysdeps/aarch64/start.S
> +++ b/sysdeps/aarch64/start.S
> @@ -46,6 +46,7 @@
> .globl _start
> .type _start,#function
> _start:
> + BTI_C
> /* Create an initial frame with 0 LR and FP */
> mov x29, #0
> mov x30, #0
OK.
> diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
> index 604c489170..086fc84b53 100644
> --- a/sysdeps/aarch64/sysdep.h
> +++ b/sysdeps/aarch64/sysdep.h
> @@ -41,12 +41,42 @@
>
> #define ASM_SIZE_DIRECTIVE(name) .size name,.-name
>
> +/* Branch Target Identitication support. */
> +#define BTI_C hint 34
> +#define BTI_J hint 36
> +
> +/* GNU_PROPERTY_AARCH64_* macros from elf.h for use in asm code. */
> +#define FEATURE_1_AND 0xc0000000
> +#define FEATURE_1_BTI 1
> +#define FEATURE_1_PAC 2
> +
> +/* Add a NT_GNU_PROPERTY_TYPE_0 note. */
> +#define GNU_PROPERTY(type, value) \
> + .section .note.gnu.property, "a"; \
> + .p2align 3; \
> + .word 4; \
> + .word 16; \
> + .word 5; \
> + .asciz "GNU"; \
> + .word type; \
> + .word 4; \
> + .word value; \
> + .word 0; \
> + .text
> +
> +/* Add GNU property note with the supported features to all asm code
> + where sysdep.h is included. */
> +#if defined HAVE_AARCH64_BTI
> +GNU_PROPERTY (FEATURE_1_AND, FEATURE_1_BTI)
> +#endif
By defining the default value as 0 I think you can check with
#if HAVE_AARCH64_BTI
> +
> /* Define an entry point visible from C. */
> #define ENTRY(name) \
> .globl C_SYMBOL_NAME(name); \
> .type C_SYMBOL_NAME(name),%function; \
> .align 4; \
> C_LABEL(name) \
> + BTI_C; \
> cfi_startproc; \
> CALL_MCOUNT
>
> @@ -56,6 +86,7 @@
> .type C_SYMBOL_NAME(name),%function; \
> .p2align align; \
> C_LABEL(name) \
> + BTI_C; \
> cfi_startproc; \
> CALL_MCOUNT
>
> @@ -68,10 +99,11 @@
> .globl C_SYMBOL_NAME(name); \
> .type C_SYMBOL_NAME(name),%function; \
> .p2align align; \
> - .rep padding; \
> + .rep padding - 1; /* -1 for bti c. */ \
> nop; \
> .endr; \
> C_LABEL(name) \
> + BTI_C; \
> cfi_startproc; \
> CALL_MCOUNT
>
>
Ok.
@@ -75,6 +75,7 @@ call_weak_fn:
.hidden _init
.type _init, %function
_init:
+ BTI_C
stp x29, x30, [sp, -16]!
mov x29, sp
#if PREINIT_FUNCTION_WEAK
@@ -89,5 +90,6 @@ _init:
.hidden _fini
.type _fini, %function
_fini:
+ BTI_C
stp x29, x30, [sp, -16]!
mov x29, sp
@@ -37,6 +37,8 @@
/* crtn.S puts function epilogues in the .init and .fini sections
corresponding to the prologues in crti.S. */
+#include <sysdep.h>
+
.section .init,"ax",%progbits
ldp x29, x30, [sp], 16
RET
@@ -74,6 +74,7 @@
cfi_startproc
.align 2
_dl_tlsdesc_return:
+ BTI_C
DELOUSE (0)
ldr PTR_REG (0), [x0, #PTR_SIZE]
RET
@@ -95,6 +96,7 @@ _dl_tlsdesc_return:
cfi_startproc
.align 2
_dl_tlsdesc_undefweak:
+ BTI_C
str x1, [sp, #-16]!
cfi_adjust_cfa_offset (16)
DELOUSE (0)
@@ -142,6 +144,7 @@ _dl_tlsdesc_undefweak:
cfi_startproc
.align 2
_dl_tlsdesc_dynamic:
+ BTI_C
DELOUSE (0)
/* Save just enough registers to support fast path, if we fall
@@ -35,6 +35,7 @@
cfi_startproc
.align 2
_dl_runtime_resolve:
+ BTI_C
/* AArch64 we get called with:
ip0 &PLTGOT[2]
ip1 temp(dl resolver entry point)
@@ -126,6 +127,7 @@ _dl_runtime_resolve:
cfi_startproc
.align 2
_dl_runtime_profile:
+ BTI_C
/* AArch64 we get called with:
ip0 &PLTGOT[2]
ip1 temp(dl resolver entry point)
@@ -46,6 +46,7 @@
.globl _start
.type _start,#function
_start:
+ BTI_C
/* Create an initial frame with 0 LR and FP */
mov x29, #0
mov x30, #0
@@ -41,12 +41,42 @@
#define ASM_SIZE_DIRECTIVE(name) .size name,.-name
+/* Branch Target Identitication support. */
+#define BTI_C hint 34
+#define BTI_J hint 36
+
+/* GNU_PROPERTY_AARCH64_* macros from elf.h for use in asm code. */
+#define FEATURE_1_AND 0xc0000000
+#define FEATURE_1_BTI 1
+#define FEATURE_1_PAC 2
+
+/* Add a NT_GNU_PROPERTY_TYPE_0 note. */
+#define GNU_PROPERTY(type, value) \
+ .section .note.gnu.property, "a"; \
+ .p2align 3; \
+ .word 4; \
+ .word 16; \
+ .word 5; \
+ .asciz "GNU"; \
+ .word type; \
+ .word 4; \
+ .word value; \
+ .word 0; \
+ .text
+
+/* Add GNU property note with the supported features to all asm code
+ where sysdep.h is included. */
+#if defined HAVE_AARCH64_BTI
+GNU_PROPERTY (FEATURE_1_AND, FEATURE_1_BTI)
+#endif
+
/* Define an entry point visible from C. */
#define ENTRY(name) \
.globl C_SYMBOL_NAME(name); \
.type C_SYMBOL_NAME(name),%function; \
.align 4; \
C_LABEL(name) \
+ BTI_C; \
cfi_startproc; \
CALL_MCOUNT
@@ -56,6 +86,7 @@
.type C_SYMBOL_NAME(name),%function; \
.p2align align; \
C_LABEL(name) \
+ BTI_C; \
cfi_startproc; \
CALL_MCOUNT
@@ -68,10 +99,11 @@
.globl C_SYMBOL_NAME(name); \
.type C_SYMBOL_NAME(name),%function; \
.p2align align; \
- .rep padding; \
+ .rep padding - 1; /* -1 for bti c. */ \
nop; \
.endr; \
C_LABEL(name) \
+ BTI_C; \
cfi_startproc; \
CALL_MCOUNT