linux-kernel - Re: [PATCH] kexec: Initialize ELF lowest address to ULONG

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Message-Id: <20250108212813.ebc0014e384e9996ab72db40@linux-foundation.org>
Date: Wed, 8 Jan 2025 21:28:13 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>
Cc: Baoquan he <bhe@...hat.com>, ebiederm@...ssion.com, Hari Bathini
 <hbathini@...ux.ibm.com>, Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
 linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX

On Thu, 9 Jan 2025 09:42:14 +0530 Sourabh Jain <sourabhjain@...ux.ibm.com> wrote:

> Hello Baoquan and Eric,
> 
> 
> On 12/12/24 08:25, Baoquan he wrote:
> > On 12/10/24 at 02:43pm, Sourabh Jain wrote:
> >> kexec_elf_load() loads an ELF executable and sets the address of the
> >> lowest PT_LOAD section to the address held by the lowest_load_addr
> >> function argument.
> >>
> >> To determine the lowest PT_LOAD address, a local variable lowest_addr
> >> (type unsigned long) is initialized to UINT_MAX. After loading each
> >> PT_LOAD, its address is compared to lowest_addr. If a loaded PT_LOAD
> >> address is lower, lowest_addr is updated. However, setting lowest_addr
> >> to UINT_MAX won't work when the kernel image is loaded above 4G, as the
> >> returned lowest PT_LOAD address would be invalid. This is resolved by
> >> initializing lowest_addr to ULONG_MAX instead.
> >>
> >> This issue was discovered while implementing crashkernel high/low
> >> reservation on the PowerPC architecture.
> >>
> >> Fixes: a0458284f062 ("powerpc: Add support code for kexec_file_load()")
> >> Cc: Baoquan he <bhe@...hat.com>
> >> Cc: Hari Bathini <hbathini@...ux.ibm.com>
> >> CC: Madhavan Srinivasan <maddy@...ux.ibm.com>
> >> Cc: Michael Ellerman <mpe@...erman.id.au>
> >> Cc: kexec@...ts.infradead.org
> >> Cc: linuxppc-dev@...ts.ozlabs.org
> >> Cc: linux-kernel@...r.kernel.org
> >> Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> >> ---
> >>   kernel/kexec_elf.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/kernel/kexec_elf.c b/kernel/kexec_elf.c
> >> index d3689632e8b9..3a5c25b2adc9 100644
> >> --- a/kernel/kexec_elf.c
> >> +++ b/kernel/kexec_elf.c
> >> @@ -390,7 +390,7 @@ int kexec_elf_load(struct kimage *image, struct elfhdr *ehdr,
> >>   			 struct kexec_buf *kbuf,
> >>   			 unsigned long *lowest_load_addr)
> >>   {
> >> -	unsigned long lowest_addr = UINT_MAX;
> >> +	unsigned long lowest_addr = ULONG_MAX;
> > Great catch.
> >
> > Acked-by: Baoquan He <bhe@...hat.com>
> Thank you for the Ack! The upcoming two patch series, which aim to 
> enable generic crashkernel reservation, depends on this fix. One of them 
> is already posted for upstream review: 
> https://lore.kernel.org/all/20250108101458.406806-1-sourabhjain@linux.ibm.com/ 
> I was wondering if you could guide us on how to get this fix pushed to 
> the mainline tree.

Please include this patch (with Baoquan's ack) in whichever tree
contains the powerpc patches which depend upon it.