linux-kernel - [PATCH v2 1/6] kexec: Initialize ELF lowest address to ULONG

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Message-ID: <20250121115442.1278458-2-sourabhjain@linux.ibm.com>
Date: Tue, 21 Jan 2025 17:24:37 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: linuxppc-dev@...ts.ozlabs.org
Cc: Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Baoquan He <bhe@...hat.com>
Subject: [PATCH v2 1/6] kexec: Initialize ELF lowest address to ULONG_MAX

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: Andrew Morton <akpm@...ux-foundation.org>
Cc: Hari Bathini <hbathini@...ux.ibm.com>
Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@...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
Acked-by: Baoquan He <bhe@...hat.com>
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;
 	int ret;
 	size_t i;

-- 
2.47.1