linux-kernel - Re: [RFC PATCH v1 04/21] RISC-V: ACPI: Enhance acpi_os

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Message-ID: <ZMy0jC55N0+nKEye@sunil-laptop>
Date:   Fri, 4 Aug 2023 13:49:24 +0530
From:   Sunil V L <sunilvl@...tanamicro.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-doc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Anup Patel <anup@...infault.org>,
        Marc Zyngier <maz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Robert Moore <robert.moore@...el.com>,
        Haibo Xu <haibo1.xu@...el.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Atish Kumar Patra <atishp@...osinc.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Alexandre Ghiti <alexghiti@...osinc.com>
Subject: Re: [RFC PATCH v1 04/21] RISC-V: ACPI: Enhance acpi_os_ioremap with
 MMIO remapping

On Fri, Aug 04, 2023 at 08:47:53AM +0300, Andy Shevchenko wrote:
> On Thu, Aug 03, 2023 at 11:28:59PM +0530, Sunil V L wrote:
> > Enhance the acpi_os_ioremap() to support opregions in MMIO
> > space. Also, have strict checks using EFI memory map
> > to allow remapping the RAM similar to arm64.
> > 
> > Cc: Ard Biesheuvel <ardb@...nel.org>
> > Cc: Alexandre Ghiti <alexghiti@...osinc.com>
> 
> You may use --cc to the command line when forming patches.
> 
> Also we usually consider Cc: as a part of the tag block, meaning no blank line
> should be here.
> 
Thanks!, Andy. I specifically wanted Ard and Alex to look at this patch
and hence added Cc. I was not aware that no blank line should be there.
Thanks for letting me know.

> > Signed-off-by: Sunil V L <sunilvl@...tanamicro.com>
> 
> ...
> 
> >  #include <linux/io.h>
> >  #include <linux/pci.h>
> >  #include <linux/efi.h>
> > +#include <linux/memblock.h>
> 
> Can you squeeze it to have some order, like to be after io.h (taking into
> account given context)?
> 
Yeah, sure. Let me update in next version.

> ...
> 
> > +			if (memblock_is_map_memory(phys) ||
> > +			    !memblock_is_region_memory(phys, size)) {
> > +				pr_warn(FW_BUG "requested region covers kernel memory @ %p\n",
> > +					&phys);
> 
> How %p can be useful here (it's mangled), but also wouldn't this give a hint to
> an attacker about the kernel memory location and diminish the KASLR protection?
> (IIRC after boot we always have the same salt for the mangling the pointers when
>  printing, so at least theoretically it might be possible to bruteforce the
>  printing algo to give a clue about the kernel address.)
> 
Okay. This is copied from arm64 version. But I think this is a good
point. Let me just print the warning message without address in the next
version.

Thanks!
Sunil