Re: [PATCH v3 3/3] powerpc/32: Add KASAN support

On Mon, Jan 21, 2019 at 9:37 AM Christophe Leroy
[off-list ref] wrote:

Le 21/01/2019 à 09:30, Dmitry Vyukov a écrit :

quoted

On Mon, Jan 21, 2019 at 8:17 AM Christophe Leroy
[off-list ref] wrote:

quoted

Le 15/01/2019 à 18:23, Andrey Ryabinin a écrit :

quoted

On 1/12/19 2:16 PM, Christophe Leroy wrote:

quoted

+KASAN_SANITIZE_early_32.o := n
+KASAN_SANITIZE_cputable.o := n
+KASAN_SANITIZE_prom_init.o := n
+

Usually it's also good idea to disable branch profiling - define DISABLE_BRANCH_PROFILING
either in top of these files or via Makefile. Branch profiling redefines if() statement and calls
instrumented ftrace_likely_update in every if().

quoted

diff --git a/arch/powerpc/mm/kasan_init.c b/arch/powerpc/mm/kasan_init.c
new file mode 100644
index 000000000000..3edc9c2d2f3e

quoted

+void __init kasan_init(void)
+{
+    struct memblock_region *reg;
+
+    for_each_memblock(memory, reg)
+            kasan_init_region(reg);
+
+    pr_info("KASAN init done\n");

Without "init_task.kasan_depth = 0;" kasan will not repot bugs.

There is test_kasan module. Make sure that it produce reports.

Thanks for the review.

Now I get the following very early in boot, what does that mean ?

This looks like an instrumented memset call before kasan shadow is
mapped, or kasan shadow is not zeros. Does this happen before or after
mapping of kasan_early_shadow_page?

This is after the mapping of kasan_early_shadow_page.

quoted

This version seems to miss what x86 code has to clear the early shadow:

/*
* kasan_early_shadow_page has been used as early shadow memory, thus
* it may contain some garbage. Now we can clear and write protect it,
* since after the TLB flush no one should write to it.
*/
memset(kasan_early_shadow_page, 0, PAGE_SIZE);

In the early part, kasan_early_shadow_page is mapped read-only so I
assumed this reset of its content was unneccessary.

I'll try with it.

Christophe

As far as I understand machine memory contains garbage after boot, and
that page needs to be all 0's so we need to explicitly memset it.

quoted

quoted

[    0.000000] KASAN init done
[    0.000000]
==================================================================
[    0.000000] BUG: KASAN: unknown-crash in memblock_alloc_try_nid+0xd8/0xf0
[    0.000000] Write of size 68 at addr c7ff5a90 by task swapper/0
[    0.000000]
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted
5.0.0-rc2-s3k-dev-00559-g88aa407c4bce #772
[    0.000000] Call Trace:
[    0.000000] [c094ded0] [c016c7e4]
print_address_description+0x1a0/0x2b8 (unreliable)
[    0.000000] [c094df00] [c016caa0] kasan_report+0xe4/0x168
[    0.000000] [c094df40] [c016b464] memset+0x2c/0x4c
[    0.000000] [c094df60] [c08731f0] memblock_alloc_try_nid+0xd8/0xf0
[    0.000000] [c094df90] [c0861f20] mmu_context_init+0x58/0xa0
[    0.000000] [c094dfb0] [c085ca70] start_kernel+0x54/0x400
[    0.000000] [c094dff0] [c0002258] start_here+0x44/0x9c
[    0.000000]
[    0.000000]
[    0.000000] Memory state around the buggy address:
[    0.000000]  c7ff5980: e2 a1 87 81 bd d4 a5 b5 f8 8d 89 e7 72 bc 20 24
[    0.000000]  c7ff5a00: e7 b9 c1 c7 17 e9 b4 bd a4 d0 e7 a0 11 15 a5 b5
[    0.000000] >c7ff5a80: b5 e1 83 a5 2d 65 31 3f f3 e5 a7 ef 34 b5 69 b5
[    0.000000]                  ^
[    0.000000]  c7ff5b00: 21 a5 c1 c1 b4 bf 2d e5 e5 c3 f5 91 e3 b8 a1 34
[    0.000000]  c7ff5b80: ad ef 23 87 3d a6 ad b5 c3 c3 80 b7 ac b1 1f 37
[    0.000000]
==================================================================
[    0.000000] Disabling lock debugging due to kernel taint
[    0.000000] MMU: Allocated 76 bytes of context maps for 16 contexts
[    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 8176
[    0.000000] Kernel command line: console=ttyCPM0,115200N8
ip=192.168.2.7:192.168.2.2::255.0.0.0:vgoip:eth0:off kgdboc=ttyCPM0
[    0.000000] Dentry cache hash table entries: 16384 (order: 2, 65536
bytes)
[    0.000000] Inode-cache hash table entries: 8192 (order: 1, 32768 bytes)
[    0.000000] Memory: 99904K/131072K available (7376K kernel code, 528K
rwdata, 1168K rodata, 576K init, 4623K bss, 31168K reserved, 0K
cma-reserved)
[    0.000000] Kernel virtual memory layout:
[    0.000000]   * 0xffefc000..0xffffc000  : fixmap
[    0.000000]   * 0xf7c00000..0xffc00000  : kasan shadow mem
[    0.000000]   * 0xf7a00000..0xf7c00000  : consistent mem
[    0.000000]   * 0xf7a00000..0xf7a00000  : early ioremap
[    0.000000]   * 0xc9000000..0xf7a00000  : vmalloc & ioremap


Christophe