Re: [PATCH] kexec: Initialize ELF lowest address to ULONG_MAX

Hello Andrew,

On 09/01/25 10:58, Andrew Morton wrote:

On Thu, 9 Jan 2025 09:42:14 +0530 Sourabh Jain [off-list ref] wrote:

quoted

Hello Baoquan and Eric,


On 12/12/24 08:25, Baoquan he wrote:

quoted

On 12/10/24 at 02:43pm, Sourabh Jain wrote:

quoted

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 <redacted>
Cc: Hari Bathini <hbathini@linux.ibm.com>
CC: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: kexec@lists.infradead.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sourabh Jain <redacted>
---
   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 <redacted>

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/ (local)
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.

Sure, I will include this patch in the respective patch series.

Thanks,
Sourabh Jain