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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <64e9a422a1ef370334b90a591229f7f4e293bf8c.1589552054.git.szabolcs.nagy@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Adhemerval Zanella via Libc-alpha Reply-To: Adhemerval Zanella Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" On 15/05/2020 11:40, Szabolcs Nagy wrote: > From: Sudakshina Das > > 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 LGTM with a small change with depends on previous commit change (with I also added a comment). Reviewed-by: Adhemerval Zanella > --- > 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 > + > .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.