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Re: [PATCH] [BZ #18134] x86-64 ld.so doesn't preserve bound registers
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Cc: Igor Zamyatin <igor dot zamyatin at intel dot com>
- Date: Wed, 18 Mar 2015 12:26:27 -0400
- Subject: Re: [PATCH] [BZ #18134] x86-64 ld.so doesn't preserve bound registers
- Authentication-results: sourceware.org; auth=none
- References: <20150316213753 dot GA20643 at intel dot com>
On 03/16/2015 05:37 PM, H.J. Lu wrote:
> We need to add a BND prefix before indirect branch at the end of
> _dl_runtime_resolve to preserve bound registers.
>
> Tested on x32, x86-64 Haswell and x86-64 Skylake. I will check it into
> master shortly and backport it to 2.21 branch.
>
> Igor, this patch doesn't fix _dl_runtime_profile. Can you take care of
> _dl_runtime_profile?
>
> Thanks.
>
>
> H.J.
> ---
> [BZ #18134]
> * sysdeps/x86_64/dl-trampoline.S (PRESERVE_BND_REGS_PREFIX): New.
> (_dl_runtime_resolve): Add a BND prefix before indirect branch.
LGTM. But yes, _dl_runtime_profile will be more work to cleanup.
> sysdeps/x86_64/dl-trampoline.S | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/sysdeps/x86_64/dl-trampoline.S b/sysdeps/x86_64/dl-trampoline.S
> index 394441d..5f9b35d 100644
> --- a/sysdeps/x86_64/dl-trampoline.S
> +++ b/sysdeps/x86_64/dl-trampoline.S
> @@ -30,6 +30,7 @@
> /* X32 saves RCX, RDX, RSI, RDI, R8 and R9 plus RAX. */
> # define REGISTER_SAVE_AREA (8 * 7)
> # define REGISTER_SAVE_RAX 0
> +# define PRESERVE_BND_REGS_PREFIX
> #else
> /* X86-64 saves RCX, RDX, RSI, RDI, R8 and R9 plus RAX as well as BND0,
> BND1, BND2, BND3. */
> @@ -40,6 +41,11 @@
> # define REGISTER_SAVE_BND2 (REGISTER_SAVE_BND1 + 16)
> # define REGISTER_SAVE_BND3 (REGISTER_SAVE_BND2 + 16)
> # define REGISTER_SAVE_RAX (REGISTER_SAVE_BND3 + 16)
> +# ifdef HAVE_MPX_SUPPORT
> +# define PRESERVE_BND_REGS_PREFIX bnd
> +# else
> +# define PRESERVE_BND_REGS_PREFIX .byte 0xf2
> +# endif
> #endif
> #define REGISTER_SAVE_RCX (REGISTER_SAVE_RAX + 8)
> #define REGISTER_SAVE_RDX (REGISTER_SAVE_RCX + 8)
> @@ -112,6 +118,8 @@ _dl_runtime_resolve:
> # Adjust stack(PLT did 2 pushes)
> addq $(REGISTER_SAVE_AREA + 16), %rsp
> cfi_adjust_cfa_offset(-(REGISTER_SAVE_AREA + 16))
> + # Preserve bound registers.
> + PRESERVE_BND_REGS_PREFIX
> jmp *%r11 # Jump to function address.
> cfi_endproc
> .size _dl_runtime_resolve, .-_dl_runtime_resolve
>