linux-kernel - Re: [PATCH 0/5] Enable pt_regs based syscalls for x86-32 native

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Date:   Fri, 21 Feb 2020 16:28:44 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Brian Gerst <brgerst@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 0/5] Enable pt_regs based syscalls for x86-32 native

On Fri, Feb 21, 2020 at 08:15:19AM -0500, Brian Gerst wrote:
> On Fri, Feb 21, 2020 at 2:07 AM Dominik Brodowski
> <linux@...inikbrodowski.net> wrote:
> >
> > Brian,
> >
> > On Fri, Feb 21, 2020 at 12:09:29AM -0500, Brian Gerst wrote:
> > > This patch series cleans up the x86 syscall wrapper code and converts
> > > the 32-bit native kernel over to pt_regs based syscalls.
> >
> > thanks for your patchset. Could you explain a bit more what the rationale
> > is. Due to asmlinkage, it doesn't leak "random user-provided register
> > content down the call chain" (as was the case for x86-64). But it may be
> > cleaner, and you mention in patch 5/5 that the new way is "a bit more
> > efficient" -- do you have numbers?
> 
> The main rationale for this patch set is to make the 32-bit native
> kernel consistent with the 64-bit kernel.  It's also slightly more
> efficient because the old code pushed all 6 arguments onto the stack
> whereas the new code only reads the args the syscall needs, with the
> pt_regs pointer passed in through a register.  By efficient I mean
> that it uses fewer instructions and stack accesses, not that it will
> actually have a significant difference on a benchmark.

OK, could you add such an explanation to the patchset then, please? Thanks,
Dominik