From 558df7209e7997275f6b8ad37737494cf2da1512 Mon Sep 17 00:00:00 2001 From: Michael Holzheu Date: Sun, 30 Oct 2011 15:16:43 +0100 Subject: [PATCH] [S390] kdump: Add infrastructure for unmapping crashkernel memory This patch introduces a mechanism that allows architecture backends to remove page tables for the crashkernel memory. This can protect the loaded kdump kernel from being overwritten by broken kernel code. Two new functions crash_map_reserved_pages() and crash_unmap_reserved_pages() are added that can be implemented by architecture code. The crash_map_reserved_pages() function is called before and crash_unmap_reserved_pages() after the crashkernel segments are loaded. The functions are also called in crash_shrink_memory() to create/remove page tables when the crashkernel memory size is reduced. To support architectures that have large pages this patch also introduces a new define KEXEC_CRASH_MEM_ALIGN. The crashkernel start and size must always be aligned with KEXEC_CRASH_MEM_ALIGN. Cc: Andrew Morton Acked-by: Vivek Goyal Signed-off-by: Michael Holzheu Signed-off-by: Martin Schwidefsky --- include/linux/kexec.h | 6 ++++++ kernel/kexec.c | 21 +++++++++++++++++++-- 2 files changed, 25 insertions(+), 2 deletions(-) diff --git a/include/linux/kexec.h b/include/linux/kexec.h index 07d9aba75562..fe45136b32cc 100644 --- a/include/linux/kexec.h +++ b/include/linux/kexec.h @@ -37,6 +37,10 @@ #define KEXEC_CRASH_CONTROL_MEMORY_LIMIT KEXEC_CONTROL_MEMORY_LIMIT #endif +#ifndef KEXEC_CRASH_MEM_ALIGN +#define KEXEC_CRASH_MEM_ALIGN PAGE_SIZE +#endif + #define KEXEC_NOTE_HEAD_BYTES ALIGN(sizeof(struct elf_note), 4) #define KEXEC_CORE_NOTE_NAME "CORE" #define KEXEC_CORE_NOTE_NAME_BYTES ALIGN(sizeof(KEXEC_CORE_NOTE_NAME), 4) @@ -133,6 +137,8 @@ extern void crash_kexec(struct pt_regs *); int kexec_should_crash(struct task_struct *); void crash_save_cpu(struct pt_regs *regs, int cpu); void crash_save_vmcoreinfo(void); +void crash_map_reserved_pages(void); +void crash_unmap_reserved_pages(void); void arch_crash_save_vmcoreinfo(void); void vmcoreinfo_append_str(const char *fmt, ...) __attribute__ ((format (printf, 1, 2))); diff --git a/kernel/kexec.c b/kernel/kexec.c index d3b8a4ceb90b..dc7bc0829286 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -999,6 +999,7 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments, kimage_free(xchg(&kexec_crash_image, NULL)); result = kimage_crash_alloc(&image, entry, nr_segments, segments); + crash_map_reserved_pages(); } if (result) goto out; @@ -1015,6 +1016,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments, goto out; } kimage_terminate(image); + if (flags & KEXEC_ON_CRASH) + crash_unmap_reserved_pages(); } /* Install the new kernel, and Uninstall the old */ image = xchg(dest_image, image); @@ -1026,6 +1029,18 @@ out: return result; } +/* + * Add and remove page tables for crashkernel memory + * + * Provide an empty default implementation here -- architecture + * code may override this + */ +void __weak crash_map_reserved_pages(void) +{} + +void __weak crash_unmap_reserved_pages(void) +{} + #ifdef CONFIG_COMPAT asmlinkage long compat_sys_kexec_load(unsigned long entry, unsigned long nr_segments, @@ -1134,14 +1149,16 @@ int crash_shrink_memory(unsigned long new_size) goto unlock; } - start = roundup(start, PAGE_SIZE); - end = roundup(start + new_size, PAGE_SIZE); + start = roundup(start, KEXEC_CRASH_MEM_ALIGN); + end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN); + crash_map_reserved_pages(); crash_free_reserved_phys_range(end, crashk_res.end); if ((start == end) && (crashk_res.parent != NULL)) release_resource(&crashk_res); crashk_res.end = end - 1; + crash_unmap_reserved_pages(); unlock: mutex_unlock(&kexec_mutex);