Subject: [PATCH v5sub1 7/8] arm64: move kernel image to base of vmalloc area

From: [email-masked] (Andrey Ryabinin)
Date: Tue, 16 Feb 2016 18:36:36 +0300

On 02/16/2016 06:17 PM, Ard Biesheuvel wrote:
> On 16 February 2016 at 13:59, Andrey Ryabinin <[email-masked]> wrote:
>>
>>
>> On 02/15/2016 09:59 PM, Catalin Marinas wrote:
>>> On Mon, Feb 15, 2016 at 05:28:02PM +0300, Andrey Ryabinin wrote:
>>>> On 02/12/2016 07:06 PM, Catalin Marinas wrote:
>>>>> So far, we have:
>>>>>
>>>>> KASAN+for-next/kernmap goes wrong
>>>>> KASAN+UBSAN goes wrong
>>>>>
>>>>> Enabled individually, KASAN, UBSAN and for-next/kernmap seem fine. I may
>>>>> have to trim for-next/core down until we figure out where the problem
>>>>> is.
>>>>>
>>>>> BUG: KASAN: stack-out-of-bounds in find_busiest_group+0x164/0x16a0 at addr ffffffc93665bc8c
>>>>
>>>> Can it be related to TLB conflicts, which supposed to be fixed in
>>>> "arm64: kasan: avoid TLB conflicts" patch from "arm64: mm: rework page
>>>> table creation" series ?
>>>
>>> I can very easily reproduce this with a vanilla 4.5-rc1 series by
>>> enabling inline instrumentation (maybe Mark's theory is true w.r.t.
>>> image size).
>>>
>>> Some information, maybe you can shed some light on this. It seems to
>>> happen only for secondary CPUs on the swapper stack (I think allocated
>>> via fork_idle()). The code generated looks sane to me, so KASAN should
>>> not complain but maybe there is some uninitialised shadow, hence the
>>> error.
>>>
>>> The report:
>>>
>>
>> Actually, the first report is a bit more useful. It shows that shadow memory was corrupted:
>>
>>   ffffffc93665bc00: f1 f1 f1 f1 00 f4 f4 f4 f2 f2 f2 f2 00 00 f1 f1
>>> ffffffc93665bc80: f1 f1 00 00 00 00 f3 f3 00 f4 f4 f4 f3 f3 f3 f3
>>                       ^
>> F1 - left redzone, it indicates start of stack frame
>> F3 - right redzone, it should be the end of stack frame.
>>
>> But here we have the second set of F1s without F3s which should close the first set of F1s.
>> Also those two F3s in the middle cannot be right.
>>
>> So shadow is corrupted.
>> Some hypotheses:
>>
>> 1) We share stack between several tasks (e.g. stack overflow, somehow corrupted SP).
>>     But this probably should cause kernel crash later, after kasan reports.
>>
>> 2) Shadow memory wasn't cleared. GCC poison memory on function entrance and unpoisons it before return.
>>      If we use some tricky way to exit from function this could cause false-positives like that.
>>      E.g. some hand-written assembly return code.
>>
>> 3) Screwed shadow mapping. I think the patch below should uncover such problem.
>> It boot-tested on qemu and didn't show any problem
>>
> 
> I think this patch gives false positive warnings in some cases:
> 
>>
>> ---
>>  arch/arm64/mm/kasan_init.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 55 insertions(+)
>>
>> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
>> index cf038c7..25d685c 100644
>> --- a/arch/arm64/mm/kasan_init.c
>> +++ b/arch/arm64/mm/kasan_init.c
>> @@ -117,6 +117,59 @@ static void __init cpu_set_ttbr1(unsigned long ttbr1)
>>         : "r" (ttbr1));
>>  }
>>
>> +static void verify_shadow(void)
>> +{
>> +       struct memblock_region *reg;
>> +       int i = 0;
>> +
>> +       for_each_memblock(memory, reg) {
>> +               void *start = (void *)__phys_to_virt(reg->base);
>> +               void *end = (void *)__phys_to_virt(reg->base + reg->size);
>> +               int *shadow_start, *shadow_end;
>> +
>> +               if (start >= end)
>> +                       break;
>> +               shadow_start = (int *)((unsigned long)kasan_mem_to_shadow(start) & ~(PAGE_SIZE - 1));
>> +               shadow_end =  (int *)kasan_mem_to_shadow(end);
> 
> shadow_start and shadow_end can refer to the same page as in the
> previous iteration. For instance, I have these two regions
> 
>   0x00006e090000-0x00006e0adfff [Conventional Memory|   |  |  |  |  |
> |   |WB|WT|WC|UC]
>   0x00006e0ae000-0x00006e0affff [Loader Data        |   |  |  |  |  |
> |   |WB|WT|WC|UC]
> 
> which are covered by different memblocks since the second one is
> marked as MEMBLOCK_NOMAP, due to the fact that it contains the UEFI
> memory map.
> 
> I get the following output
> 
> kasan: screwed shadow mapping 23575, 23573
> 
> which I think is simply a result from the fact the shadow_start refers
> to the same page as in the previous iteration(s)
> 

You are right. 
So we should write 'shadow_start' instead of 'i'.

---
 arch/arm64/mm/kasan_init.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index cf038c7..ee035c2 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -117,6 +117,55 @@ static void __init cpu_set_ttbr1(unsigned long ttbr1)
 	: "r" (ttbr1));
 }
 
+static void verify_shadow(void)
+{
+	struct memblock_region *reg;
+
+	for_each_memblock(memory, reg) {
+		void *start = (void *)__phys_to_virt(reg->base);
+		void *end = (void *)__phys_to_virt(reg->base + reg->size);
+		unsigned long *shadow_start, *shadow_end;
+
+		if (start >= end)
+			break;
+		shadow_start = (unsigned long *)kasan_mem_to_shadow(start);
+		shadow_end =  (unsigned long *)kasan_mem_to_shadow(end);
+		for (; shadow_start < shadow_end; shadow_start += PAGE_SIZE/sizeof(unsigned long)) {
+			*shadow_start = (unsigned long)shadow_start;
+		}
+	}
+
+	for_each_memblock(memory, reg) {
+		void *start = (void *)__phys_to_virt(reg->base);
+		void *end = (void *)__phys_to_virt(reg->base + reg->size);
+		unsigned long *shadow_start, *shadow_end;
+
+		if (start >= end)
+			break;
+		shadow_start = (unsigned long *)kasan_mem_to_shadow(start);
+		shadow_end =  (unsigned long *)kasan_mem_to_shadow(end);
+		for (; shadow_start < shadow_end; shadow_start += PAGE_SIZE/sizeof(unsigned long)) {
+			if (*shadow_start != (unsigned long)shadow_start) {
+				pr_err("screwed shadow mapping %lx, %lx\n", *shadow_start, (unsigned long)shadow_start);
+				goto clear;
+			}
+		}
+	}
+clear:
+	for_each_memblock(memory, reg) {
+		void *start = (void *)__phys_to_virt(reg->base);
+		void *end = (void *)__phys_to_virt(reg->base + reg->size);
+		unsigned long shadow_start, shadow_end;
+
+		if (start >= end)
+			break;
+		shadow_start =  (unsigned long)kasan_mem_to_shadow(start);
+		shadow_end =  (unsigned long)kasan_mem_to_shadow(end);
+		memset((void *)shadow_start, 0, shadow_end - shadow_start);
+	}
+
+}
+
 void __init kasan_init(void)
 {
 	struct memblock_region *reg;
@@ -159,6 +208,8 @@ void __init kasan_init(void)
 	cpu_set_ttbr1(__pa(swapper_pg_dir));
 	flush_tlb_all();
 
+	verify_shadow();
+
 	/* At this point kasan is fully initialized. Enable error messages */
 	init_task.kasan_depth = 0;
 	pr_info("KernelAddressSanitizer initialized\n");
--