diff options
authorLee, Chun-Yi <joeyli.kernel@gmail.com>2015-09-29 20:58:57 +0800
committerIngo Molnar <mingo@kernel.org>2015-10-02 09:13:06 +0200
commite3c41e37b0f4b18cbd4dac76cbeece5a7558b909 (patch)
parent95c632f4e4e6365a20397f4fd04dcf27aab02958 (diff)
x86/kexec: Fix kexec crash in syscall kexec_file_load()
The original bug is a page fault crash that sometimes happens on big machines when preparing ELF headers: BUG: unable to handle kernel paging request at ffffc90613fc9000 IP: [<ffffffff8103d645>] prepare_elf64_ram_headers_callback+0x165/0x260 The bug is caused by us under-counting the number of memory ranges and subsequently not allocating enough ELF header space for them. The bug is typically masked on smaller systems, because the ELF header allocation is rounded up to the next page. This patch modifies the code in fill_up_crash_elf_data() by using walk_system_ram_res() instead of walk_system_ram_range() to correctly count the max number of crash memory ranges. That's because the walk_system_ram_range() filters out small memory regions that reside in the same page, but walk_system_ram_res() does not. Here's how I found the bug: After tracing prepare_elf64_headers() and prepare_elf64_ram_headers_callback(), the code uses walk_system_ram_res() to fill-in crash memory regions information to the program header, so it counts those small memory regions that reside in a page area. But, when the kernel was using walk_system_ram_range() in fill_up_crash_elf_data() to count the number of crash memory regions, it filters out small regions. I printed those small memory regions, for example: kexec: Get nr_ram ranges. vaddr=0xffff880077592258 paddr=0x77592258, sz=0xdc0 Based on the code in walk_system_ram_range(), this memory region will be filtered out: pfn = (0x77592258 + 0x1000 - 1) >> 12 = 0x77593 end_pfn = (0x77592258 + 0xfc0 -1 + 1) >> 12 = 0x77593 end_pfn - pfn = 0x77593 - 0x77593 = 0 <=== if (end_pfn > pfn) is FALSE So, the max_nr_ranges that's counted by the kernel doesn't include small memory regions - causing us to under-allocate the required space. That causes the page fault crash that happens in a later code path when preparing ELF headers. This bug is not easy to reproduce on small machines that have few CPUs, because the allocated page aligned ELF buffer has more free space to cover those small memory regions' PT_LOAD headers. Signed-off-by: Lee, Chun-Yi <jlee@suse.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Baoquan He <bhe@redhat.com> Cc: Jiang Liu <jiang.liu@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Takashi Iwai <tiwai@suse.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: kexec@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/1443531537-29436-1-git-send-email-jlee@suse.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 files changed, 3 insertions, 4 deletions
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index e068d6683dba..74ca2fe7a0b3 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -185,10 +185,9 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
-static int get_nr_ram_ranges_callback(unsigned long start_pfn,
- unsigned long nr_pfn, void *arg)
+static int get_nr_ram_ranges_callback(u64 start, u64 end, void *arg)
- int *nr_ranges = arg;
+ unsigned int *nr_ranges = arg;
return 0;
@@ -214,7 +213,7 @@ static void fill_up_crash_elf_data(struct crash_elf_data *ced,
ced->image = image;
- walk_system_ram_range(0, -1, &nr_ranges,
+ walk_system_ram_res(0, -1, &nr_ranges,
ced->max_nr_ranges = nr_ranges;