linux-kernel - Re: System Call trashing registers

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Message-ID: <ZOy3+8qKfQxyrWez@duo.ucw.cz>
Date:   Mon, 28 Aug 2023 17:06:35 +0200
From:   Pavel Machek <pavel@....cz>
To:     Joshua Hudson <joshudson@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: System Call trashing registers

Hi!

> 1) A lot of my old 32-bit programs don't work on x64 linux anymore
> because int 80h now trashes ecx and edx. This hasn't been a serious
> problem for me.
> 
> 2) syscall is documented to trash rcx and r11.
> 
> What I don't understand is why this hasn't ever led to a security
> issue due to leaking values from kernel space (in the trashed
> registers) back to userspace.

I guess you should cc x86 maintainers?

I guess this is a regression? When did it start?

BR,
								Pavel
-- 
People of Russia, stop Putin before his war on Ukraine escalates.

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