[PATCH 5.4 170/177] s390/kaslr: store KASLR offset for early dumps

Greg Kroah-Hartman
2019-12-16T18:21:25Z

From: Gerald Schaefer <gerald.schaefer@de.ibm.com>

commit a9f2f6865d784477e1c7b59269d3a384abafd9ca upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/boot/startup.c | 5 +++++
arch/s390/kernel/machine_kexec.c | 2 +-
2 files changed, 6 insertions(+), 1 deletion(-)

--- 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);
--- a/arch/s390/kernel/machine_kexec.c
+++ b/arch/s390/kernel/machine_kexec.c
@@ -254,10 +254,10 @@ 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)