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Date:   Tue, 12 Jan 2021 18:45:08 +0100
From:   Oleg Nesterov <>
To:     Michal Hocko <>
Cc:     Suren Baghdasaryan <>,,,,,,,,,,,,,,
Subject: Re: [PATCH v2 1/1] mm/madvise: replace ptrace attach requirement for

On 01/12, Michal Hocko wrote:
> On Mon 11-01-21 09:06:22, Suren Baghdasaryan wrote:
> > What we want is the ability for one process to influence another process
> > in order to optimize performance across the entire system while leaving
> > the security boundary intact.
> > Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ
> > and CAP_SYS_NICE. PTRACE_MODE_READ to prevent leaking ASLR metadata
> > and CAP_SYS_NICE for influencing process performance.
> I have to say that ptrace modes are rather obscure to me. So I cannot
> really judge whether MODE_READ is sufficient. My understanding has
> always been that this is requred to RO access to the address space. But
> this operation clearly has a visible side effect. Do we have any actual
> documentation for the existing modes?
> I would be really curious to hear from Jann and Oleg (now Cced).

Can't comment, sorry. I never understood these security checks and never tried.
IIUC only selinux/etc can treat ATTACH/READ differently and I have no idea what
is the difference.


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