linux-kernel - Re: [PATCH 2/2] x86: vdso: Remove redundant ifdeffery around in_ia32

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <8734m7d1bt.fsf@email.froward.int.ebiederm.org>
Date: Tue, 10 Sep 2024 09:34:46 -0500
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>,  Ingo Molnar <mingo@...hat.com>,
  Borislav Petkov <bp@...en8.de>,  Dave Hansen
 <dave.hansen@...ux.intel.com>,  x86@...nel.org,  "H. Peter Anvin"
 <hpa@...or.com>,  Kees Cook <kees@...nel.org>,  Thomas Gleixner
 <tglx@...utronix.de>,  linux-kernel@...r.kernel.org,  linux-mm@...ck.org
Subject: Re: [PATCH 2/2] x86: vdso: Remove redundant ifdeffery around
 in_ia32_syscall()

Thomas Weißschuh <thomas.weissschuh@...utronix.de> writes:

> The ifdefs only guard code that is also guarded by in_ia32_syscall(),
> which already contains the same ifdefs itself.
>
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> ---
>  arch/x86/entry/vdso/vma.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 9059b9d96393..ab2b011471e0 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -75,7 +75,6 @@ static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
>  static void vdso_fix_landing(const struct vdso_image *image,
>  		struct vm_area_struct *new_vma)
>  {
> -#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
>  	if (in_ia32_syscall() && image == &vdso_image_32) {
>  		struct pt_regs *regs = current_pt_regs();
>  		unsigned long vdso_land = image->sym_int80_landing_pad;
> @@ -86,7 +85,6 @@ static void vdso_fix_landing(const struct vdso_image *image,
>  		if (regs->ip == old_land_addr)
>  			regs->ip = new_vma->vm_start + vdso_land;
>  	}
> -#endif
>  }
>  
>  static int vdso_mremap(const struct vm_special_mapping *sm,
> @@ -339,7 +337,6 @@ int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
>  
>  bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
>  {
> -#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
>  	const struct vdso_image *image = current->mm->context.vdso_image;
>  	unsigned long vdso = (unsigned long) current->mm->context.vdso;
>  
> @@ -348,7 +345,6 @@ bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
>  		    regs->ip == vdso + image->sym_vdso32_rt_sigreturn_landing_pad)
>  			return true;
>  	}
> -#endif
>  	return false;
>  }

Have you tested to verify that after this change
arch_syscall_is_vdso_signature compiles out the "image" and "vdso"
variables?

If the compilers don't it might be worth it rearrange the code as:
	if (in_ia32_syscall()) {
		const struct vdso_image *image = current->mm->context.vdso_image;
		unsigned long vdso = (unsigned long) current->mm->context.vdso;

		if (image == &vdso_image_32) {
                	....
                        return true;
                }
	}
        return false.

Making the variables depend upon in_ia32_syscall() so you can be certain
they are compiles out.

Eric