linux-kernel - Re: [PATCH] resource,kexec: walk_system_ram_res

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Message-ID: <67117918aa217_10a0a294dc@dwillia2-mobl3.amr.corp.intel.com.notmuch>
Date: Thu, 17 Oct 2024 13:52:40 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Gregory Price <gourry@...rry.net>, <kexec@...ts.infradead.org>
CC: <linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
	<bhelgaas@...gle.com>, <andriy.shevchenko@...ux.intel.com>,
	<ilpo.jarvinen@...ux.intel.com>, <mika.westerberg@...ux.intel.com>,
	<ying.huang@...el.com>, <bhe@...hat.com>, <gourry@...rry.net>,
	<tglx@...utronix.de>, <takahiro.akashi@...aro.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] resource,kexec: walk_system_ram_res_rev must retain
 resource flags

Gregory Price wrote:
> walk_system_ram_res_rev() erroneously discards resource flags when
> passing the information to the callback.
> 
> This causes systems with IORESOURCE_SYSRAM_DRIVER_MANAGED memory to
> have these resources selected during kexec to store kexec buffers
> if that memory happens to be at placed above normal system ram.
> 
> This leads to undefined behavior after reboot. If the kexec buffer
> is never touched, nothing happens. If the kexec buffer is touched,
> it could lead to a crash (like below) or undefined behavior.
> 
> Tested on a system with CXL memory expanders with driver managed
> memory, TPM enabled, and CONFIG_IMA_KEXEC=y. Adding printk's
> showed the flags were being discarded and as a result the check
> for IORESOURCE_SYSRAM_DRIVER_MANAGED passes.
> 
> find_next_iomem_res: name(System RAM (kmem))
> 		     start(10000000000)
> 		     end(1034fffffff)
> 		     flags(83000200)
> 
> locate_mem_hole_top_down: start(10000000000) end(1034fffffff) flags(0)
> 
[..]
> Link: https://lore.kernel.org/all/20231114091658.228030-1-bhe@redhat.com/
> Fixes: 7acf164b259d ("resource: add walk_system_ram_res_rev()")
> Cc: stable@...r.kernel.org
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>  kernel/resource.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index b730bd28b422..4101016e8b20 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -459,9 +459,7 @@ int walk_system_ram_res_rev(u64 start, u64 end, void *arg,
>  			rams_size += 16;
>  		}
>  
> -		rams[i].start = res.start;
> -		rams[i++].end = res.end;
> -
> +		rams[i++] = res;
>  		start = res.end + 1;

Looks good to me, makes it obvious that everything that
find_next_iomem_res() would return for walk_system_ram_range() users is
the same as what walk_system_ram_res_rev() returns.

Reviewed-by: Dan Williams <dan.j.williams@...el.com>