[Crash-utility] Re: Fix irq_stack_size on ARM64

[yp z <wonderzyp@xxxxxxxxx>]

Hi Lianbo and Tao,

Thank you for your suggestions, and I have rewrote a patch in two cases:

[1] with vmcoreinfo:

+       if (kernel_symbol_exists("kasan_enable_current")) {
+               min_thread_shift += 1;
+               thread_shift = (min_thread_shift < machdep->pageshift) ? machdep->pageshift : min_thread_shift;
+       }

BTW:  can you help point out the current issue is with or without the vmcoreinfo? Yeping

My issue is with vmcoreinfo of "SYMBOL("kasan_enable_current")", and works well with this patch.

[2] without vmcoreinfo: 

What about somehow the disassembly gives us hex values like:
#0xe? It won't work by then. Any ideas for this?

 In order to use stol() as expected, I have changed the first non-numeric char to '\0':

+                       if ((pos1 = strstr(buf1, "tbnz"))) {
+                               if ((pos2 = strchr(pos1, '#'))) {
+                                       pos2 += 1;
+                                       pos1 = pos2;
+                                       while (*pos2 != '\0') {
+                                               if (!((*pos2 >= '0' && *pos2 <= '9')
+                                                       || (*pos2 >= 'A' && *pos2 <= 'F')
+                                                       || (*pos2 >= 'a' && *pos2 <= 'f'))) {
+                                                       *pos2 = '\0';
+                                                       break;
+                                               }
+                                               ++pos2;
+                                       }
+                                       thread_shift = stol(pos1, RETURN_ON_ERROR|QUIET, &errflag);

Thanks.

Yeping.ZHENG

lijiang <lijiang@xxxxxxxxxx> 于2024年7月26日周五 17:23写道：

On Fri, Jul 19, 2024 at 6:40 AM Tao Liu <ltao@xxxxxxxxxx> wrote:

Hi Lianbo,

On Thu, Jul 18, 2024 at 10:50 PM Lianbo Jiang <lijiang@xxxxxxxxxx> wrote:
>
> On 7/16/24 4:22 PM, Tao Liu wrote:
>
> > Hi Yeping,
> >
> > Thanks for the fix.
> >
> > On Thu, Jul 11, 2024 at 1:38 PM <wonderzyp@xxxxxxxxx> wrote:
> >> When using the crash tool to parse the ARM64 dump file with KASAN enabled, I found that using the bt -a command will cause this tool to crash, the following is the backtrace infomation.
> >>
> >> (gdb) bt
> >> #0  0x00005635ac2b166b in arm64_unwind_frame (frame=0x7ffdaf35cb70, bt=0x7ffdaf35d430)
> >>      at arm64.c:2821
> >> #1  arm64_back_trace_cmd (bt=0x7ffdaf35d430) at arm64.c:3306
> >> #2  0x00005635ac27b108 in back_trace (bt=bt@entry=0x7ffdaf35d430) at kernel.c:3239
> >> #3  0x00005635ac2880ae in cmd_bt () at kernel.c:2863
> >> #4  0x00005635ac1f16dc in exec_command () at main.c:893
> >> #5  0x00005635ac1f192a in main_loop () at main.c:840
> >> #6  0x00005635ac50df81 in captured_main (data="" out>) at main.c:1284
> >> #7  gdb_main (args=<optimized out>) at main.c:1313
> >> #8  0x00005635ac50e000 in gdb_main_entry (argc=<optimized out>, argv=<optimized out>)
> >>      at main.c:1338
> >> #9  0x00005635ac1ea2a5 in main (argc=5, argv=0x7ffdaf35dde8) at main.c:721
> >> Eventually, I found that it was may caused by not setting irq_stack_size properly, and provide this patch to solve it.
> >>
> > Could you please re-draft your commit message? The original one looks
> > informal. E.g:
> >
> > A segfault issue was observed on KASAN enabled arm64 kernel due to the
> > incorrect irq_stack_size, see the following stack trace:
> > ...
> > The issue was caused by ...., and this patch will fix the issue by ....
> >
> >>  From 34b28aa8c11e77d20adec4f7705a14d239c8a55f Mon Sep 17 00:00:00 2001
> >> From: wonderzyp <wonderzyp@xxxxxx>
> >> Date: Mon, 8 Jul 2024 20:11:38 +0800
> >> Subject: [PATCH 1131/1131] set_arm64_irq_stack_size
> >>
> >> Signed-off-by: Yeping Zheng <wonderzyp@xxxxxxxxx>
> >> ---
> >>   arm64.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
> >>   1 file changed, 47 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arm64.c b/arm64.c
> >> index b3040d7..39d891b 100644
> >> --- a/arm64.c
> >> +++ b/arm64.c
> >> @@ -93,6 +93,7 @@ static void arm64_calc_VA_BITS(void);
> >>   static int arm64_is_uvaddr(ulong, struct task_context *);
> >>   static void arm64_calc_KERNELPACMASK(void);
> >>   static int arm64_get_vmcoreinfo(unsigned long *vaddr, const char *label, int base);
> >> +static ulong arm64_set_irq_stack_size(struct machine_specific *ms);
> >>
> >>   struct kernel_range {
> >>          unsigned long modules_vaddr, modules_end;
> >> @@ -2223,8 +2224,14 @@ arm64_irq_stack_init(void)
> >>                  if (MEMBER_EXISTS("thread_union", "stack")) {
> >>                          if ((sz = MEMBER_SIZE("thread_union", "stack")) > 0)
> >>                                  ms->irq_stack_size = sz;
> >> -               } else
> >> -                       ms->irq_stack_size = ARM64_IRQ_STACK_SIZE;
> >> +               } else {
> >> +                       ulong res = arm64_set_irq_stack_size(ms);
> >> +                       if (res > 0){
> >> +                               ms->irq_stack_size = res;
> >> +                       } else {
> >> +                               ms->irq_stack_size = ARM64_IRQ_STACK_SIZE;
> >> +                       }
> >> +               }
> >>
> >>                  machdep->flags |= IRQ_STACKS;
> >>
> >> @@ -4921,6 +4928,44 @@ static void arm64_calc_KERNELPACMASK(void)
> >>          }
> >>   }
> >>
> >> +static ulong arm64_set_irq_stack_size(struct machine_specific *ms)
> >> +{
> >> +       char *string;
> >> +       int ret;
> >> +       int KASAN_THREAD_SHIFT = 0;
> >> +       int MIN_THREAD_SHIFT;
> >> +       ulong ARM64_PAGE_SHIFT;
> >> +       ulong THREAD_SHIFT = 0;
> >> +       ulong THREAD_SIZE;
> > I guess the upper case of variable names is not encouraged, though it
> > is the variable that comes from kernel config file.
> >
> >> +       if (kt->ikconfig_flags & IKCONFIG_AVAIL) {
> >> +               if ((ret = get_kernel_config("CONFIG_KASAN_GENERIC", NULL) == IKCONFIG_Y) ||
> >> +                       (ret = get_kernel_config("CONFIG_KASAN_SW_TAGS", NULL) == IKCONFIG_Y)) {
> >> +                               KASAN_THREAD_SHIFT = 1;
> >> +                       }
> >> +       }
> >> +       MIN_THREAD_SHIFT = 14 + KASAN_THREAD_SHIFT;
> >> +
> >> +       if (kt->ikconfig_flags & IKCONFIG_AVAIL) {
> > Could the if condition be merged with the prior one?
> >
> >> +               if ((ret = get_kernel_config("CONFIG_VMAP_STACK", NULL)) == IKCONFIG_Y){
> >> +                       if ((ret = get_kernel_config("CONFIG_ARM64_PAGE_SHIFT", &string)) ==
>
> The "CONFIG_ARM64_PAGE_SHIFT " has been removed since kernel v6.9-rc1,
> so this can not work on the latest kernel. See:
>
> d3e5bab923d3 ("arch: simplify architecture specific page size
> configuration")
>
>
> In addition, the IKCONFIG is not available in most distributions,  it
> can not cover this case. There is a similar discussion there:
>
> https://www.mail-archive.com/devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx/msg00880.html
>
> Can you try to handle the current issue with a similar solution?
>
>
> >> IKCONFIG_STR){
> >> +                               ARM64_PAGE_SHIFT = atol(string);
> >> +                       }
> >> +                       if (MIN_THREAD_SHIFT < ARM64_PAGE_SHIFT){
> >> +                               THREAD_SHIFT = ARM64_PAGE_SHIFT;
> >> +                       } else {
> >> +                               THREAD_SHIFT = MIN_THREAD_SHIFT;
> >> +                       }
> >> +               }
> >> +       }
> >> +
> >> +       if (THREAD_SHIFT == 0) {
> >> +               return -1;
> >> +       }
> >> +
> >> +       THREAD_SIZE = ((1UL) << THREAD_SHIFT);
> >> +       return THREAD_SIZE;
> >> +}
> > I'm OK with the approach above, since it directly came from the kernel
> > source. However I'm not a fan of checking kernel configs, there might
> > be kernels which are compiled without CONFIG_IKCONFIG.
> >
> > Could we add an approach here, to get the value from disassembly when
> > CONFIG_IKCONFIG is negative?
> >
> > kernel source: arch/arm64/kernel/entry.S:
> >
> > .macro kernel_ventry, el:req, ht:req, regsize:req, label:req
> > ....
> > add sp, sp, x0 // sp' = sp + x0
> > sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp
> > tbnz x0, #THREAD_SHIFT, 0f <<<<<<<<
> >
> > $ objdump -d vmlinux
> > ...
> > ffff800080010800 <vectors>:
> > ffff800080010800:       d10543ff        sub     sp, sp, #0x150
> > ffff800080010804:       8b2063ff        add     sp, sp, x0
> > ffff800080010808:       cb2063e0        sub     x0, sp, x0
> > ffff80008001080c:       37800080        tbnz    w0, #16,
> > ffff80008001081c <vectors+0x1c> <<<<<<<<<<
> >
> > It is easy to get the THREAD_SHIFT value by disassembling the tbnz
> > instruction. What do you think @Lianbo Jiang
>
> This is a good idea, but it still relies on compiler.
>
> As we discussed, usually I would recommend finding its values via some
> kernel symbols.

Yeah, but I didn't find a suitable symbol so far... In addition, the

It's true. For the KASAN, it is easy to find a suitable symbol, but it's not easy for the PAGESIZE or PAGESHIFT.

Given that I would suggest covering two cases:

[1] with vmcoreinfo(see mm/kasan/common.c)

...

int min_thread_shift = 14;

if (kernel_symbol_exists("kasan_enable_current"))

    min_thread_shift += 1;

thread_shift = (min_thread_shift < machdep->pageshift) ? machdep->pageshift : min_thread_shift;

...

[2] without vmcoreinfo

Use Tao's solution(disassemble kernel code)

The first one is better than the second one in case of having vmcoreinfo, If I understand correctly.

But we still need to cover the above two cases in the crash tools.

BTW:  can you help point out the current issue is with or without the vmcoreinfo? Yeping

Thanks

Lianbo

above case is a little different here, the tbnz instruction is not
generated from C code, it is written in assembly in
arch/arm64/kernel/entry.S file. So I guess there would be a lower
possibility if tbnz instruction gets replaced or eliminated by the
compilers. Anyway, it's OK to me if you don't want to accept the
approach.

Thanks,
Tao Liu


>
>
> Thanks
>
> Lianbo
>
> >
> > Thanks,
> > Tao Liu
> >
> >> +
> >>   #endif  /* ARM64 */
> >>
> >>
> >> --
> >> 2.25.1
> >>
>

From b48cd074345673694c4b8bf3a6ad496760ea562c Mon Sep 17 00:00:00 2001
From: "yeping.zheng" <yeping.zheng@xxxxxxx>
Date: Mon, 29 Jul 2024 09:27:16 +0800
Subject: [PATCH] Subject: [PATCH] A segfault issue due to the incorrect irq_stack_size on ARM64

See the following stack trace:
(gdb) bt
 #0  0x00005635ac2b166b in arm64_unwind_frame (frame=0x7ffdaf35cb70, bt=0x7ffdaf35d430) at arm64.c:2821
 #1  arm64_back_trace_cmd (bt=0x7ffdaf35d430) at arm64.c:3306
 #2  0x00005635ac27b108 in back_trace (bt=bt@entry=0x7ffdaf35d430) at kernel.c:3239
 #3  0x00005635ac2880ae in cmd_bt () at kernel.c:2863
 #4  0x00005635ac1f16dc in exec_command () at main.c:893
 #5  0x00005635ac1f192a in main_loop () at main.c:840
 #6  0x00005635ac50df81 in captured_main (data=<optimized out>) at main.c:1284
 #7  gdb_main (args=<optimized out>) at main.c:1313
 #8  0x00005635ac50e000 in gdb_main_entry (argc=<optimized out>, argv=<optimized out>) at main.c:1338
 #9  0x00005635ac1ea2a5 in main (argc=5, argv=0x7ffdaf35dde8) at main.c:721

The issue may be encountered when thread_union symbol not found in vmlinux
due to compiling optimization.

This patch will try the following 2 methods to get the irq_stack_size
when thread_union symbol unavailable:

1. Try getting the value from IKconfig.
2. Try getting the value from kernel code disassembly, to get
   THREAD_SHIFT directly from tbnz instruction.

In arch/arm64/kernel/entry.S:

.macro kernel_ventry, el:req, ht:req, regsize:req, label:req
...
        add     sp, sp, x0
        sub     x0, sp, x0
        tbnz    x0, #THREAD_SHIFT, 0f

$ gdb vmlinux
(gdb) disass vectors
Dump of assembler code for function vectors:
   ...
   0xffff800080010804 <+4>:     add     sp, sp, x0
   0xffff800080010808 <+8>:     sub     x0, sp, x0
   0xffff80008001080c <+12>:    tbnz    w0, #16, 0xffff80008001081c <vectors+28>

Signed-off-by: yeping.zheng <yeping.zheng(a)nio.com&gt;
---
 arm64.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 56 insertions(+), 3 deletions(-)

diff --git a/arm64.c b/arm64.c
index 78e6609..26f4153 100644
--- a/arm64.c
+++ b/arm64.c
@@ -94,6 +94,7 @@ static int arm64_is_uvaddr(ulong, struct task_context *);
 static void arm64_calc_KERNELPACMASK(void);
 static void arm64_recalc_KERNELPACMASK(void);
 static int arm64_get_vmcoreinfo(unsigned long *vaddr, const char *label, int base);
+static ulong arm64_set_irq_stack_size(void);
 
 struct kernel_range {
 	unsigned long modules_vaddr, modules_end;
@@ -2234,8 +2235,10 @@ arm64_irq_stack_init(void)
 		if (MEMBER_EXISTS("thread_union", "stack")) { 
 			if ((sz = MEMBER_SIZE("thread_union", "stack")) > 0)
 				ms->irq_stack_size = sz;
-		} else
-			ms->irq_stack_size = ARM64_IRQ_STACK_SIZE;
+		} else {
+			ulong res = arm64_set_irq_stack_size();
+			ms->irq_stack_size = (res > 0) ? res : ARM64_IRQ_STACK_SIZE;
+		}
 
 		machdep->flags |= IRQ_STACKS;
 
@@ -4950,6 +4953,56 @@ static void arm64_recalc_KERNELPACMASK(void){
 	}
 }
 
-#endif  /* ARM64 */
+static ulong arm64_set_irq_stack_size(void)
+{
+	char *string;
+	int min_thread_shift = 14;
+	ulong thread_shift = 0;
 
+	char buf1[BUFSIZE];
+	char *pos1, *pos2;
+	int errflag = 0;
+
+	if (kernel_symbol_exists("kasan_enable_current")) {
+		min_thread_shift += 1;
+		thread_shift = (min_thread_shift < machdep->pageshift) ? machdep->pageshift : min_thread_shift;
+	} else {
+		sprintf(buf1, "x/32i vectors");
+		open_tmpfile();
+		if (!gdb_pass_through(buf1, pc->tmpfile, GNU_RETURN_ON_ERROR)) {
+			goto out;
+		}
+		rewind(pc->tmpfile);
+		while (fgets(buf1, BUFSIZE, pc->tmpfile)) {
+			if ((pos1 = strstr(buf1, "tbnz"))) {
+				if ((pos2 = strchr(pos1, '#'))) {
+					pos2 += 1;
+					pos1 = pos2;
+					while (*pos2 != '\0') {
+						if (!((*pos2 >= '0' && *pos2 <= '9')
+							|| (*pos2 >= 'A' && *pos2 <= 'F')
+							|| (*pos2 >= 'a' && *pos2 <= 'f'))) {
+							*pos2 = '\0';
+							break;
+						}
+						++pos2;
+					}
+					thread_shift = stol(pos1, RETURN_ON_ERROR|QUIET, &errflag);
+					if (errflag) {
+						thread_shift = 0;
+					}
+					break;
+				}
+			}
+		}
+out:
+		close_tmpfile();
+	}
+
+	if (!thread_shift)
+		return 0;
+	else
+		return ((1UL) << thread_shift);
+}
 
+#endif  /* ARM64 */
\ No newline at end of file
-- 
2.25.1

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