Messages in this thread | | | From | "Metzger, Markus T" <> | Subject | RE: [PATCH 14/15] x86/fsgsbase/64: Support legacy behavior when FS/GS updated by ptracer | Date | Wed, 21 Mar 2018 07:01:54 +0000 |
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> -----Original Message----- > From: Andy Lutomirski [mailto:luto@kernel.org] > Sent: 21 March 2018 01:47
Hello Andy,
> I retract this particular comment. But I still think that all this complexity needs to > be more clearly justified. My objection to the old approach wasn't that I thought > it was obviously wrong -- I thought that someone needed to survey existing > ptrace() users and see if anyone needed the fancier code that you're adding. Did > you find something that needs this fancy code?
There are 3 cases: - only FS changed, e.g. "p $fs = ..." - only FS_BASE changed, e.g. "p $fs_base = ..." - both change, e.g. "p foo()" when restoring the original register state on return from the inferior call
The ptracer may use SETREGS in all 3 cases, even though only a single register changed.
For case 1, it might make sense to change FS_BASE as a side-effect. For case 2, we'd only want to change FS_BASE and leave FS. For case 3, we'd want both FS and FS_BASE to be set to the ptracer-provided values.
Does that make sense?
Thanks, Markus.
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