[v2,08/13] aarch64: fix RTLD_START for BTI

Message ID 3b7c87b1784c8b610686c1dd9bc881a60ffaa788.1589277641.git.szabolcs.nagy@arm.com
State Superseded
Headers show
Series
  • aarch64: branch protection support
Related show

Commit Message

Szabolcs Nagy May 12, 2020, 10:14 a.m.
Tailcalls must use x16 or x17 for the indirect branch instruction
to be compatible with code that uses BTI c at function entries.
(Other forms of indirect branches can only land on BTI j.)

Also added a BTI c at the ELF entry point of rtld, this is not
strictly necessary since the kernel does not use indirect branch
to get there, but it seems safest once building glibc itself with
BTI is supported.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

---
 sysdeps/aarch64/dl-machine.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

-- 
2.17.1

Comments

Andreas Schwab May 12, 2020, 10:29 a.m. | #1
On Mai 12 2020, Szabolcs Nagy wrote:

> diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h

> index db3335e5ad..70b9ed3925 100644

> --- a/sysdeps/aarch64/dl-machine.h

> +++ b/sysdeps/aarch64/dl-machine.h

> @@ -125,6 +125,8 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)

>  .globl _dl_start_user							\n\

>  .type _dl_start_user, %function						\n\

>  _start:									\n\

> +	// bti c							\n\

> +	hint	34							\n\


BTI_C?

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."
Szabolcs Nagy May 12, 2020, 11:36 a.m. | #2
The 05/12/2020 12:29, Andreas Schwab wrote:
> On Mai 12 2020, Szabolcs Nagy wrote:

> 

> > diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h

> > index db3335e5ad..70b9ed3925 100644

> > --- a/sysdeps/aarch64/dl-machine.h

> > +++ b/sysdeps/aarch64/dl-machine.h

> > @@ -125,6 +125,8 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)

> >  .globl _dl_start_user							\n\

> >  .type _dl_start_user, %function						\n\

> >  _start:									\n\

> > +	// bti c							\n\

> > +	hint	34							\n\

> 

> BTI_C?


this is c code with inline asm, BTI_C is used in asm files.

Patch

diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
index db3335e5ad..70b9ed3925 100644
--- a/sysdeps/aarch64/dl-machine.h
+++ b/sysdeps/aarch64/dl-machine.h
@@ -125,6 +125,8 @@  elf_machine_runtime_setup (struct link_map *l, int lazy, int profile)
 .globl _dl_start_user							\n\
 .type _dl_start_user, %function						\n\
 _start:									\n\
+	// bti c							\n\
+	hint	34							\n\
 	mov	" PTR "0, " PTR_SP "					\n\
 	bl	_dl_start						\n\
 	// returns user entry point in x0				\n\
@@ -178,7 +180,8 @@  _dl_start_user:								\n\
 	adrp	x0, _dl_fini						\n\
 	add	" PTR "0, " PTR "0, #:lo12:_dl_fini			\n\
 	// jump to the user_s entry point				\n\
-	br      x21							\n\
+	mov     x16, x21						\n\
+	br      x16							\n\
 ");
 
 #define elf_machine_type_class(type)					\