[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <5b536d60-d130-4061-984e-3b83a3cab092@intel.com>
Date: Fri, 22 Mar 2024 08:40:56 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>,
linux-kernel@...r.kernel.org
Cc: x86@...nel.org, dave.hansen@...ux.intel.com, tglx@...utronix.de,
matthias.neugschwandtner@...cle.com, andrew.brownsword@...cle.com
Subject: Re: [RFC PATCH v2 1/1] x86/pkeys: update PKRU to enable pkey 0 before
XSAVE
On 3/21/24 14:56, Aruna Ramakrishna wrote:
> +/*
> + * Ensure that the both the current stack and the alternate signal
> + * stack is writeable. The alternate stack must be accessible by the
> + * init PKRU value.
> + */
> +static inline u32 sig_prepare_pkru(void)
> +{
> + u32 current_pkru = read_pkru();
> + u32 init_pkru_snapshot = pkru_get_init_value();
> +
> + write_pkru(current_pkru & init_pkru_snapshot);
> + return current_pkru;
> +}
That comment is quite misleading. This code has *ZERO* knowledge of the
permissions on either the current or alternate stack. It _assumes_ that
the current PKRU permissions allow writes to the current stack and
_assumes_ that the init PKRU value can write to the alternative stack.
Those aren't bad assumptions, but they _are_ assumptions and need to be
clearly called out as such.
The '&' operation looks rather random and needs an explanation. What is
that logically trying to do? It's trying to clear bits in the old
(pre-signal) PKRU value so that it gains write access to the alt stack.
Please say that.
Which leads me to ask: Why bother with the '&'? It would be simpler to,
for instance, just wrpkru(0). What is being written to the old stack at
this point?
I also dislike something being called 'current_pkru' when it's clearly
the old value by the time it is returned.
> +static inline void sig_restore_pkru(u32 pkru)
> +{
> + write_pkru(pkru);
> +}
This seems like unnecessary abstraction.
Powered by blists - more mailing lists