s390/kaslr: store KASLR offset for early dumps

The KASLR offset is added to vmcoreinfo in arch_crash_save_vmcoreinfo(),
so that it can be found by crash when processing kernel dumps.

However, arch_crash_save_vmcoreinfo() is called during a subsys_initcall,
so if the kernel crashes before that, we have no vmcoreinfo and no KASLR
offset.

Fix this by storing the KASLR offset in the lowcore, where the vmcore_info
pointer will be stored, and where it can be found by crash. In order to
make it distinguishable from a real vmcore_info pointer, mark it as uneven
(KASLR offset itself is aligned to THREAD_SIZE).

When arch_crash_save_vmcoreinfo() stores the real vmcore_info pointer in
the lowcore, it overwrites the KASLR offset. At that point, the KASLR
offset is not yet added to vmcoreinfo, so we also need to move the
mem_assign_absolute() behind the vmcoreinfo_append_str().

Fixes: b2d24b97b2a9 ("s390/kernel: add support for kernel address space layout randomization (KASLR)")
Cc: <stable@vger.kernel.org> # v5.2+
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index fbd341e..3b3a11f 100644 (file)
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -170,6 +170,11 @@ void startup_kernel(void)
                handle_relocs(__kaslr_offset);
 
        if (__kaslr_offset) {
+               /*
+                * Save KASLR offset for early dumps, before vmcore_info is set.
+                * Mark as uneven to distinguish from real vmcore_info pointer.
+                */
+               S390_lowcore.vmcore_info = __kaslr_offset | 0x1UL;
                /* Clear non-relocated kernel */
                if (IS_ENABLED(CONFIG_KERNEL_UNCOMPRESSED))
                        memset(img, 0, vmlinux.image_size);

diff --git a/arch/s390/kernel/machine_kexec.c b/arch/s390/kernel/machine_kexec.c
index dcaadce..cb8b1cc 100644 (file)
--- a/arch/s390/kernel/machine_kexec.c
+++ b/arch/s390/kernel/machine_kexec.c
@@ -256,10 +256,10 @@ void arch_crash_save_vmcoreinfo(void)
        VMCOREINFO_SYMBOL(lowcore_ptr);
        VMCOREINFO_SYMBOL(high_memory);
        VMCOREINFO_LENGTH(lowcore_ptr, NR_CPUS);
-       mem_assign_absolute(S390_lowcore.vmcore_info, paddr_vmcoreinfo_note());
        vmcoreinfo_append_str("SDMA=%lx\n", __sdma);
        vmcoreinfo_append_str("EDMA=%lx\n", __edma);
        vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
+       mem_assign_absolute(S390_lowcore.vmcore_info, paddr_vmcoreinfo_note());
 }
 
 void machine_shutdown(void)