linux-kernel - Re: [PATCH 3/6] x86/entry/vdso32: remove int80_landing

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Message-ID: <CAMzpN2g1G9Jc6eL4L+Rq3kGvKALt-tuaA3NKUuZ-jJXeaKuPRA@mail.gmail.com>
Date: Wed, 29 Oct 2025 02:54:43 -0400
From: Brian Gerst <brgerst@...il.com>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>, "Peter Zijlstra (Intel)" <peterz@...radead.org>, "Theodore Ts'o" <tytso@....edu>, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
	Xin Li <xin@...or.com>, Andrew Cooper <andrew.cooper3@...rix.com>, 
	Andy Lutomirski <luto@...nel.org>, Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, 
	James Morse <james.morse@....com>, Jarkko Sakkinen <jarkko@...nel.org>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Kees Cook <kees@...nel.org>, Nam Cao <namcao@...utronix.de>, 
	Oleg Nesterov <oleg@...hat.com>, Perry Yuan <perry.yuan@....com>, 
	Thomas Gleixner <tglx@...utronix.de>, Thomas Huth <thuth@...hat.com>, Uros Bizjak <ubizjak@...il.com>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-sgx@...r.kernel.org, 
	x86@...nel.org
Subject: Re: [PATCH 3/6] x86/entry/vdso32: remove int80_landing_pad

On Sun, Oct 26, 2025 at 6:12 PM H. Peter Anvin <hpa@...or.com> wrote:
>
> There is no fundamental reason for the int80_landing_pad symbol. If ip
> falls within the vdso, and the vdso is moved, we should change the ip
> accordingly, regardless of mode or location within the vdso. This
> *currently* can only happen on 32 bits, but there isn't any reason not
> to do so generically.
>
> Note that if this is ever possible from a vdso-internal call, then the
> user space stack will also needed to be adjusted (as well as the
> shadow stack, if enabled.) Fortunately this is not currently the case.
>
> At the moment, we don't even consider other threads when moving the
> vdso. The assumption is that it is only used by process freeze/thaw
> for migration, where this is not an issue.
>
> Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
> ---
>  arch/x86/entry/vdso/vdso32/system_call.S |  1 -
>  arch/x86/entry/vdso/vma.c                | 16 ++++++----------
>  arch/x86/tools/vdso2c.c                  |  1 -
>  3 files changed, 6 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S
> index 2a15634bbe75..d14eca4403c5 100644
> --- a/arch/x86/entry/vdso/vdso32/system_call.S
> +++ b/arch/x86/entry/vdso/vdso32/system_call.S
> @@ -62,7 +62,6 @@ __kernel_vsyscall:
>
>         /* Enter using int $0x80 */
>         int     $0x80
> -SYM_INNER_LABEL(int80_landing_pad, SYM_L_GLOBAL)

This is still needed by do_fast_syscall_32().


Brian Gerst