linux-kernel - System Call trashing registers

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Message-ID: <CA+jjjYQWeqDY3EFQWmVzV2pXyhfRaHm6s-XWYSXfe1CxvkeuEQ@mail.gmail.com>
Date:   Thu, 24 Aug 2023 09:15:15 -0700
From:   Joshua Hudson <joshudson@...il.com>
To:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: System Call trashing registers

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.