[PATCH v5 1/2] x86/crash: reserve elfcorehdr for CONFIG_NR_CPUS, not CONFIG_NR_CPUS_DEFAULT

[Ionut Nechita (Wind River)]

From: Ionut Nechita <ionut.nechita at windriver.com>

NR_CPUS_DEFAULT is purely a Kconfig thing.  Its entire purpose in life is
to start NR_CPUS at a sane value.  There is precisely one (buggy)
reference to it outside of Kconfig in the whole kernel: the x86 crash
code.

That code undersizes the elfcorehdr reservation whenever NR_CPUS exceeds
NR_CPUS_DEFAULT, because the header carries one phdr per possible CPU and
num_possible_cpus() is bounded by NR_CPUS.  kexec_file_load(2) then fails
with -EINVAL from sanity_check_segment_list(), and kexec_load(2) silently
truncates the elfcorehdr, which surfaces later as a bad or unusable dump.

Size the elfcorehdr reservation with NR_CPUS instead.

Fixes: ea53ad9cf73b ("x86/crash: add x86 crash hotplug support")
Assisted-by: LLM
Signed-off-by: Ionut Nechita <ionut.nechita at windriver.com>
Reviewed-by: Jinjie Ruan <ruanjinjie at huawei.com>
Reviewed-by: Bradley Morgan <brads at mainlining.org>
Reviewed-by: Sourabh Jain <sourabhjain at linux.ibm.com>
Acked-by: Baoquan He <baoquan.he at linux.dev>
---
 arch/x86/kernel/crash.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index e681ec9cf1dc..e6f23933a6df 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -369,9 +369,9 @@ int crash_load_segments(struct kimage *image)
 	 * maximum CPUs and maximum memory ranges.
 	 */
 	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
-		pnum = 2 + CONFIG_NR_CPUS_DEFAULT + CONFIG_CRASH_MAX_MEMORY_RANGES;
+		pnum = 2 + CONFIG_NR_CPUS + CONFIG_CRASH_MAX_MEMORY_RANGES;
 	else
-		pnum += 2 + CONFIG_NR_CPUS_DEFAULT;
+		pnum += 2 + CONFIG_NR_CPUS;
 
 	if (pnum < (unsigned long)PN_XNUM) {
 		kbuf.memsz = pnum * sizeof(Elf64_Phdr);
@@ -430,7 +430,7 @@ unsigned int arch_crash_get_elfcorehdr_size(void)
 	unsigned int sz;
 
 	/* kernel_map, VMCOREINFO and maximum CPUs */
-	sz = 2 + CONFIG_NR_CPUS_DEFAULT;
+	sz = 2 + CONFIG_NR_CPUS;
 	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
 		sz += CONFIG_CRASH_MAX_MEMORY_RANGES;
 	sz *= sizeof(Elf64_Phdr);

base-commit: 89c07d98716a13454ec3fd9f97689e812cc71bd4
-- 
2.55.0