6.12-stable review patch. If anyone has any objections, please let me know.
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From: Sourabh Jain sourabhjain@linux.ibm.com
commit 00fbff75c5acb4755f06f08bd1071879c63940c5 upstream.
When crashkernel is configured with a high reservation, shrinking its value below the low crashkernel reservation causes two issues:
1. Invalid crashkernel resource objects 2. Kernel crash if crashkernel shrinking is done twice
For example, with crashkernel=200M,high, the kernel reserves 200MB of high memory and some default low memory (say 256MB). The reservation appears as:
cat /proc/iomem | grep -i crash af000000-beffffff : Crash kernel 433000000-43f7fffff : Crash kernel
If crashkernel is then shrunk to 50MB (echo 52428800 > /sys/kernel/kexec_crash_size), /proc/iomem still shows 256MB reserved: af000000-beffffff : Crash kernel
Instead, it should show 50MB: af000000-b21fffff : Crash kernel
Further shrinking crashkernel to 40MB causes a kernel crash with the following trace (x86):
BUG: kernel NULL pointer dereference, address: 0000000000000038 PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI <snip...> Call Trace: <TASK> ? __die_body.cold+0x19/0x27 ? page_fault_oops+0x15a/0x2f0 ? search_module_extables+0x19/0x60 ? search_bpf_extables+0x5f/0x80 ? exc_page_fault+0x7e/0x180 ? asm_exc_page_fault+0x26/0x30 ? __release_resource+0xd/0xb0 release_resource+0x26/0x40 __crash_shrink_memory+0xe5/0x110 crash_shrink_memory+0x12a/0x190 kexec_crash_size_store+0x41/0x80 kernfs_fop_write_iter+0x141/0x1f0 vfs_write+0x294/0x460 ksys_write+0x6d/0xf0 <snip...>
This happens because __crash_shrink_memory()/kernel/crash_core.c incorrectly updates the crashk_res resource object even when crashk_low_res should be updated.
Fix this by ensuring the correct crashkernel resource object is updated when shrinking crashkernel memory.
Link: https://lkml.kernel.org/r/20251101193741.289252-1-sourabhjain@linux.ibm.com Fixes: 16c6006af4d4 ("kexec: enable kexec_crash_size to support two crash kernel regions") Signed-off-by: Sourabh Jain sourabhjain@linux.ibm.com Acked-by: Baoquan He bhe@redhat.com Cc: Zhen Lei thunder.leizhen@huawei.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/crash_core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -352,7 +352,7 @@ static int __crash_shrink_memory(struct old_res->start = 0; old_res->end = 0; } else { - crashk_res.end = ram_res->start - 1; + old_res->end = ram_res->start - 1; }
crash_free_reserved_phys_range(ram_res->start, ram_res->end);