linux-kernel - Re: [PATCH v4] x86/entry_32: Use stack segment selector for VERW operand

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Message-ID: <m2A7GXQAIf62-3nxzvPWE28Spw3Jn2JuIgtsZbMrXN2HF-mZwtMOQ7BKcrmRD3A_nocJYD8YgnFmC9kK0CONp8DxzZnuvBq6D3vaYFsBRUQ=@protonmail.com>
Date: Thu, 11 Jul 2024 06:52:22 +0000
From: Jari Ruusu <jariruusu@...tonmail.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, linux-kernel@...r.kernel.org, x86@...nel.org, Robert Gill <rtgill82@...il.com>, Brian Gerst <brgerst@...il.com>, "Linux regression tracking (Thorsten Leemhuis)" <regressions@...mhuis.info>, antonio.gomez.iglesias@...ux.intel.com, daniel.sneddon@...ux.intel.com, stable@...r.kernel.org
Subject: Re: [PATCH v4] x86/entry_32: Use stack segment selector for VERW operand

On Wednesday, July 10th, 2024 at 22:06, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> wrote:
> Fixes: a0e2dab44d22 ("x86/entry_32: Add VERW just before userspace transition")
> Cc: stable@...r.kernel.org # 5.10+
> Reported-by: Robert Gill rtgill82@...il.com
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218707
> Closes: https://lore.kernel.org/all/8c77ccfd-d561-45a1-8ed5-6b75212c7a58@leemhuis.info/
> Suggested-by: Dave Hansen dave.hansen@...ux.intel.com
> Suggested-by: Brian Gerst brgerst@...il.com # Use %ss
> Signed-off-by: Pawan Gupta pawan.kumar.gupta@...ux.intel.com
> 
> v4:
> - Further simplify the patch by using %ss for all VERW calls in 32-bit mode (Brian).
> - In NMI exit path move VERW after RESTORE_ALL_NMI that touches GPRs (Dave).
> 
> v3: https://lore.kernel.org/r/20240701-fix-dosemu-vm86-v3-1-b1969532c75a@linux.intel.com
> - Simplify CLEAR_CPU_BUFFERS_SAFE by using %ss instead of %ds (Brian).
> - Do verw before popf in SYSEXIT path (Jari).
> 
> v2: https://lore.kernel.org/r/20240627-fix-dosemu-vm86-v2-1-d5579f698e77@linux.intel.com
> - Safe guard against any other system calls like vm86() that might change %ds (Dave).
> 
> v1: https://lore.kernel.org/r/20240426-fix-dosemu-vm86-v1-1-88c826a3f378@linux.intel.com

Pawan,
Your patch looks OK to me.

Greg,
I have verified that patch hunks go correct places on
kernel.org linux-5.10.221, linux-6.1.97 and linux-6.6.38
kernels. All tests run inside 32-bit VM. The patch fixes
show-stopper issues with virtual-8086 mode and dosemu. Once
the patch is accepted upstream, it should go to all 5.10+
stable kernels.

--
Jari Ruusu  4096R/8132F189 12D6 4C3A DCDA 0AA4 27BD  ACDF F073 3C80 8132 F189