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Re: Build warnings in Xen 5.15.y and 5.10.y with retbleed backports
- To: Juergen Gross <jgross@xxxxxxxx>, Nicolai Stange <nstange@xxxxxxx>, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Mon, 18 Jul 2022 09:36:26 -0400
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, "H. Peter Anvin" <hpa@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, jpoimboe@xxxxxxxxxx, Ben Hutchings <ben@xxxxxxxxxxxxxxx>
- Delivery-date: Mon, 18 Jul 2022 13:37:08 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 7/17/22 1:20 AM, Juergen Gross wrote:
What about filling the complete hypercall page just with "int 3" or "ud2"?
Any try to do a hypercall before the hypercall page has been initialized
is a bug anyway. What good can come from calling a function which will
return a basically random value instead of doing a privileged operation?
This is all about objtool, that's why 'ret' was added there originally by f4b4bc10b0b8
("x86/xen: Support objtool vmlinux.o validation in xen-head.S").
Before that it was all 'nop' which is similar to what you are suggesting
('int3' or 'ud2' would of course be better)
-boris
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