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From: Brian Gerst <brgerst@gmail.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: "the arch/x86 maintainers" <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Juergen Gross <jgross@suse.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH 3/6] x86/entry/64/compat: Fix Xen PV SYSENTER frame setup
Date: Wed, 1 Jul 2020 11:42:37 -0400	[thread overview]
Message-ID: <CAMzpN2iW4XD1Gsgq0ZeeH2eewLO+9Mk6eyk0LnbF-kP3v=smLg@mail.gmail.com> (raw)
In-Reply-To: <947880c41ade688ff4836f665d0c9fcaa9bd1201.1593191971.git.luto@kernel.org>

On Fri, Jun 26, 2020 at 1:30 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> The SYSENTER frame setup was nonsense.  It worked by accident
> because the normal code into which the Xen asm jumped
> (entry_SYSENTER_32/compat) threw away SP without touching the stack.
> entry_SYSENTER_compat was recently modified such that it relied on
> having a valid stack pointer, so now the Xen asm needs to invoke it
> with a valid stack.
>
> Fix it up like SYSCALL: use the Xen-provided frame and skip the bare
> metal prologue.
>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: xen-devel@lists.xenproject.org
> Fixes: 1c3e5d3f60e2 ("x86/entry: Make entry_64_compat.S objtool clean")
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/x86/entry/entry_64_compat.S |  1 +
>  arch/x86/xen/xen-asm_64.S        | 20 ++++++++++++++++----
>  2 files changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index 7b9d8150f652..381a6de7de9c 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -79,6 +79,7 @@ SYM_CODE_START(entry_SYSENTER_compat)
>         pushfq                          /* pt_regs->flags (except IF = 0) */
>         pushq   $__USER32_CS            /* pt_regs->cs */
>         pushq   $0                      /* pt_regs->ip = 0 (placeholder) */
> +SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)

This skips over the section that truncates the syscall number to
32-bits.  The comments present some doubt that it is actually
necessary, but the Xen path shouldn't differ from native.  That code
should be moved after this new label.

--
Brian Gerst

  parent reply	other threads:[~2020-07-01 15:42 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-26 17:21 [PATCH 0/6] x86/entry: Fixes Andy Lutomirski
2020-06-26 17:21 ` [PATCH 1/6] x86/entry: Assert that syscalls are on the right stack Andy Lutomirski
2020-07-01  8:04   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-07-06 14:34   ` [PATCH] x86/entry: Mark check_user_regs() noinstr Peter Zijlstra
2020-06-26 17:21 ` [PATCH 2/6] x86/entry: Move SYSENTER's regs->sp and regs->flags fixups into C Andy Lutomirski
2020-07-01  8:04   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-06-26 17:21 ` [PATCH 3/6] x86/entry/64/compat: Fix Xen PV SYSENTER frame setup Andy Lutomirski
2020-06-28  2:47   ` Boris Ostrovsky
2020-07-01  8:04   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-07-01 15:42   ` Brian Gerst [this message]
2020-07-01 18:39     ` [PATCH 3/6] " Andy Lutomirski
2020-07-02 12:54       ` Thomas Gleixner
2020-06-26 17:21 ` [PATCH 4/6] selftests/x86/syscall_nt: Add more flag combinations Andy Lutomirski
2020-07-01  8:04   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-06-26 17:21 ` [PATCH 5/6] selftests/x86/syscall_nt: Clear weird flags after each test Andy Lutomirski
2020-07-01  8:04   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2020-06-26 17:21 ` [PATCH 6/6] selftests/x86: Consolidate and fix get/set_eflags() helpers Andy Lutomirski
2020-07-01  8:04   ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski

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