arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()

[PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()

Posted by Tengda Wu 6 months, 2 weeks ago

KASAN reports a stack-out-of-bounds read in regs_get_kernel_stack_nth().

Call Trace:
[   97.283505] BUG: KASAN: stack-out-of-bounds in regs_get_kernel_stack_nth+0xa8/0xc8
[   97.284677] Read of size 8 at addr ffff800089277c10 by task 1.sh/2550
[   97.285732]
[   97.286067] CPU: 7 PID: 2550 Comm: 1.sh Not tainted 6.6.0+ #11
[   97.287032] Hardware name: linux,dummy-virt (DT)
[   97.287815] Call trace:
[   97.288279]  dump_backtrace+0xa0/0x128
[   97.288946]  show_stack+0x20/0x38
[   97.289551]  dump_stack_lvl+0x78/0xc8
[   97.290203]  print_address_description.constprop.0+0x84/0x3c8
[   97.291159]  print_report+0xb0/0x280
[   97.291792]  kasan_report+0x84/0xd0
[   97.292421]  __asan_load8+0x9c/0xc0
[   97.293042]  regs_get_kernel_stack_nth+0xa8/0xc8
[   97.293835]  process_fetch_insn+0x770/0xa30
[   97.294562]  kprobe_trace_func+0x254/0x3b0
[   97.295271]  kprobe_dispatcher+0x98/0xe0
[   97.295955]  kprobe_breakpoint_handler+0x1b0/0x210
[   97.296774]  call_break_hook+0xc4/0x100
[   97.297451]  brk_handler+0x24/0x78
[   97.298073]  do_debug_exception+0xac/0x178
[   97.298785]  el1_dbg+0x70/0x90
[   97.299344]  el1h_64_sync_handler+0xcc/0xe8
[   97.300066]  el1h_64_sync+0x78/0x80
[   97.300699]  kernel_clone+0x0/0x500
[   97.301331]  __arm64_sys_clone+0x70/0x90
[   97.302084]  invoke_syscall+0x68/0x198
[   97.302746]  el0_svc_common.constprop.0+0x11c/0x150
[   97.303569]  do_el0_svc+0x38/0x50
[   97.304164]  el0_svc+0x44/0x1d8
[   97.304749]  el0t_64_sync_handler+0x100/0x130
[   97.305500]  el0t_64_sync+0x188/0x190
[   97.306151]
[   97.306475] The buggy address belongs to stack of task 1.sh/2550
[   97.307461]  and is located at offset 0 in frame:
[   97.308257]  __se_sys_clone+0x0/0x138
[   97.308910]
[   97.309241] This frame has 1 object:
[   97.309873]  [48, 184) 'args'
[   97.309876]
[   97.310749] The buggy address belongs to the virtual mapping at
[   97.310749]  [ffff800089270000, ffff800089279000) created by:
[   97.310749]  dup_task_struct+0xc0/0x2e8
[   97.313347]
[   97.313674] The buggy address belongs to the physical page:
[   97.314604] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x14f69a
[   97.315885] flags: 0x15ffffe00000000(node=1|zone=2|lastcpupid=0xfffff)
[   97.316957] raw: 015ffffe00000000 0000000000000000 dead000000000122 0000000000000000
[   97.318207] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
[   97.319445] page dumped because: kasan: bad access detected
[   97.320371]
[   97.320694] Memory state around the buggy address:
[   97.321511]  ffff800089277b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   97.322681]  ffff800089277b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   97.323846] >ffff800089277c00: 00 00 f1 f1 f1 f1 f1 f1 00 00 00 00 00 00 00 00
[   97.325023]                          ^
[   97.325683]  ffff800089277c80: 00 00 00 00 00 00 00 00 00 f3 f3 f3 f3 f3 f3 f3
[   97.326856]  ffff800089277d00: f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00

This issue seems to be related to the behavior of some gcc compilers and
was also fixed on the s390 architecture before:

 commit d93a855c31b7 ("s390/ptrace: Avoid KASAN false positives in regs_get_kernel_stack_nth()")

As described in that commit, regs_get_kernel_stack_nth() has confirmed that
`addr` is on the stack, so reading the value at `*addr` should be allowed.
Use READ_ONCE_NOCHECK() helper to silence the KASAN check for this case.

Fixes: 0a8ea52c3eb1 ("arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature")
Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
---
 arch/arm64/kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index f79b0d5f71ac..fe3f7e554d14 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -141,7 +141,7 @@ unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
 
 	addr += n;
 	if (regs_within_kernel_stack(regs, (unsigned long)addr))
-		return *addr;
+		return READ_ONCE_NOCHECK(addr);
 	else
 		return 0;
 }
-- 
2.34.1

Re: [PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()

Posted by Will Deacon 6 months, 1 week ago

On Wed, 04 Jun 2025 00:55:33 +0000, Tengda Wu wrote:
> KASAN reports a stack-out-of-bounds read in regs_get_kernel_stack_nth().
> 
> Call Trace:
> [   97.283505] BUG: KASAN: stack-out-of-bounds in regs_get_kernel_stack_nth+0xa8/0xc8
> [   97.284677] Read of size 8 at addr ffff800089277c10 by task 1.sh/2550
> [   97.285732]
> [   97.286067] CPU: 7 PID: 2550 Comm: 1.sh Not tainted 6.6.0+ #11
> [   97.287032] Hardware name: linux,dummy-virt (DT)
> [   97.287815] Call trace:
> [   97.288279]  dump_backtrace+0xa0/0x128
> [   97.288946]  show_stack+0x20/0x38
> [   97.289551]  dump_stack_lvl+0x78/0xc8
> [   97.290203]  print_address_description.constprop.0+0x84/0x3c8
> [   97.291159]  print_report+0xb0/0x280
> [   97.291792]  kasan_report+0x84/0xd0
> [   97.292421]  __asan_load8+0x9c/0xc0
> [   97.293042]  regs_get_kernel_stack_nth+0xa8/0xc8
> [   97.293835]  process_fetch_insn+0x770/0xa30
> [   97.294562]  kprobe_trace_func+0x254/0x3b0
> [   97.295271]  kprobe_dispatcher+0x98/0xe0
> [   97.295955]  kprobe_breakpoint_handler+0x1b0/0x210
> [   97.296774]  call_break_hook+0xc4/0x100
> [   97.297451]  brk_handler+0x24/0x78
> [   97.298073]  do_debug_exception+0xac/0x178
> [   97.298785]  el1_dbg+0x70/0x90
> [   97.299344]  el1h_64_sync_handler+0xcc/0xe8
> [   97.300066]  el1h_64_sync+0x78/0x80
> [   97.300699]  kernel_clone+0x0/0x500
> [   97.301331]  __arm64_sys_clone+0x70/0x90
> [   97.302084]  invoke_syscall+0x68/0x198
> [   97.302746]  el0_svc_common.constprop.0+0x11c/0x150
> [   97.303569]  do_el0_svc+0x38/0x50
> [   97.304164]  el0_svc+0x44/0x1d8
> [   97.304749]  el0t_64_sync_handler+0x100/0x130
> [   97.305500]  el0t_64_sync+0x188/0x190
> [   97.306151]
> [   97.306475] The buggy address belongs to stack of task 1.sh/2550
> [   97.307461]  and is located at offset 0 in frame:
> [   97.308257]  __se_sys_clone+0x0/0x138
> [   97.308910]
> [   97.309241] This frame has 1 object:
> [   97.309873]  [48, 184) 'args'
> [   97.309876]
> [   97.310749] The buggy address belongs to the virtual mapping at
> [   97.310749]  [ffff800089270000, ffff800089279000) created by:
> [   97.310749]  dup_task_struct+0xc0/0x2e8
> [   97.313347]
> [   97.313674] The buggy address belongs to the physical page:
> [   97.314604] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x14f69a
> [   97.315885] flags: 0x15ffffe00000000(node=1|zone=2|lastcpupid=0xfffff)
> [   97.316957] raw: 015ffffe00000000 0000000000000000 dead000000000122 0000000000000000
> [   97.318207] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
> [   97.319445] page dumped because: kasan: bad access detected
> [   97.320371]
> [   97.320694] Memory state around the buggy address:
> [   97.321511]  ffff800089277b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [   97.322681]  ffff800089277b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [   97.323846] >ffff800089277c00: 00 00 f1 f1 f1 f1 f1 f1 00 00 00 00 00 00 00 00
> [   97.325023]                          ^
> [   97.325683]  ffff800089277c80: 00 00 00 00 00 00 00 00 00 f3 f3 f3 f3 f3 f3 f3
> [   97.326856]  ffff800089277d00: f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 
> [...]

Applied (using *addr) to arm64 (for-next/fixes), thanks!

[1/1] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()
      https://git.kernel.org/arm64/c/39dfc971e42d

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

Re: [PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()

Posted by Will Deacon 6 months, 1 week ago

On Wed, Jun 04, 2025 at 12:55:33AM +0000, Tengda Wu wrote:
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index f79b0d5f71ac..fe3f7e554d14 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -141,7 +141,7 @@ unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
>  
>  	addr += n;
>  	if (regs_within_kernel_stack(regs, (unsigned long)addr))
> -		return *addr;
> +		return READ_ONCE_NOCHECK(addr);

I think this should be '*addr', but that makes me wonder wtf s390 is
doing...

Will

Re: [PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()

Posted by Tengda Wu 6 months ago


On 2025/6/13 0:33, Will Deacon wrote:
> On Wed, Jun 04, 2025 at 12:55:33AM +0000, Tengda Wu wrote:
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index f79b0d5f71ac..fe3f7e554d14 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -141,7 +141,7 @@ unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
>>  
>>  	addr += n;
>>  	if (regs_within_kernel_stack(regs, (unsigned long)addr))
>> -		return *addr;
>> +		return READ_ONCE_NOCHECK(addr);
> 
> I think this should be '*addr', but that makes me wonder wtf s390 is
> doing...
> 
> Will

Sorry, I just received this email as there have been some issues
with my mailbox recently. I was about to send the v2 version with
the '*' mark, but I found out you have already fixed and applied
it to the linux-next. Thank you for your tolerance.

Tengda

Re: [PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()

Posted by Heiko Carstens 6 months, 1 week ago

On Thu, Jun 12, 2025 at 05:33:32PM +0100, Will Deacon wrote:
> On Wed, Jun 04, 2025 at 12:55:33AM +0000, Tengda Wu wrote:
> > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> > index f79b0d5f71ac..fe3f7e554d14 100644
> > --- a/arch/arm64/kernel/ptrace.c
> > +++ b/arch/arm64/kernel/ptrace.c
> > @@ -141,7 +141,7 @@ unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
> >  
> >  	addr += n;
> >  	if (regs_within_kernel_stack(regs, (unsigned long)addr))
> > -		return *addr;
> > +		return READ_ONCE_NOCHECK(addr);
> 
> I think this should be '*addr', but that makes me wonder wtf s390 is
> doing...

That's obviously a brown paper bag bug in our code... will be fixed.

Re: [PATCH -next] arm64/ptrace: Fix stack-out-of-bounds read in regs_get_kernel_stack_nth()

Posted by Tengda Wu 6 months, 1 week ago

Ping?

Thanks,
Tengda

On 2025/6/4 8:55, Tengda Wu wrote:
> KASAN reports a stack-out-of-bounds read in regs_get_kernel_stack_nth().
> 
> Call Trace:
> [   97.283505] BUG: KASAN: stack-out-of-bounds in regs_get_kernel_stack_nth+0xa8/0xc8
> [   97.284677] Read of size 8 at addr ffff800089277c10 by task 1.sh/2550
> [   97.285732]
> [   97.286067] CPU: 7 PID: 2550 Comm: 1.sh Not tainted 6.6.0+ #11
> [   97.287032] Hardware name: linux,dummy-virt (DT)
> [   97.287815] Call trace:
> [   97.288279]  dump_backtrace+0xa0/0x128
> [   97.288946]  show_stack+0x20/0x38
> [   97.289551]  dump_stack_lvl+0x78/0xc8
> [   97.290203]  print_address_description.constprop.0+0x84/0x3c8
> [   97.291159]  print_report+0xb0/0x280
> [   97.291792]  kasan_report+0x84/0xd0
> [   97.292421]  __asan_load8+0x9c/0xc0
> [   97.293042]  regs_get_kernel_stack_nth+0xa8/0xc8
> [   97.293835]  process_fetch_insn+0x770/0xa30
> [   97.294562]  kprobe_trace_func+0x254/0x3b0
> [   97.295271]  kprobe_dispatcher+0x98/0xe0
> [   97.295955]  kprobe_breakpoint_handler+0x1b0/0x210
> [   97.296774]  call_break_hook+0xc4/0x100
> [   97.297451]  brk_handler+0x24/0x78
> [   97.298073]  do_debug_exception+0xac/0x178
> [   97.298785]  el1_dbg+0x70/0x90
> [   97.299344]  el1h_64_sync_handler+0xcc/0xe8
> [   97.300066]  el1h_64_sync+0x78/0x80
> [   97.300699]  kernel_clone+0x0/0x500
> [   97.301331]  __arm64_sys_clone+0x70/0x90
> [   97.302084]  invoke_syscall+0x68/0x198
> [   97.302746]  el0_svc_common.constprop.0+0x11c/0x150
> [   97.303569]  do_el0_svc+0x38/0x50
> [   97.304164]  el0_svc+0x44/0x1d8
> [   97.304749]  el0t_64_sync_handler+0x100/0x130
> [   97.305500]  el0t_64_sync+0x188/0x190
> [   97.306151]
> [   97.306475] The buggy address belongs to stack of task 1.sh/2550
> [   97.307461]  and is located at offset 0 in frame:
> [   97.308257]  __se_sys_clone+0x0/0x138
> [   97.308910]
> [   97.309241] This frame has 1 object:
> [   97.309873]  [48, 184) 'args'
> [   97.309876]
> [   97.310749] The buggy address belongs to the virtual mapping at
> [   97.310749]  [ffff800089270000, ffff800089279000) created by:
> [   97.310749]  dup_task_struct+0xc0/0x2e8
> [   97.313347]
> [   97.313674] The buggy address belongs to the physical page:
> [   97.314604] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x14f69a
> [   97.315885] flags: 0x15ffffe00000000(node=1|zone=2|lastcpupid=0xfffff)
> [   97.316957] raw: 015ffffe00000000 0000000000000000 dead000000000122 0000000000000000
> [   97.318207] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
> [   97.319445] page dumped because: kasan: bad access detected
> [   97.320371]
> [   97.320694] Memory state around the buggy address:
> [   97.321511]  ffff800089277b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [   97.322681]  ffff800089277b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [   97.323846] >ffff800089277c00: 00 00 f1 f1 f1 f1 f1 f1 00 00 00 00 00 00 00 00
> [   97.325023]                          ^
> [   97.325683]  ffff800089277c80: 00 00 00 00 00 00 00 00 00 f3 f3 f3 f3 f3 f3 f3
> [   97.326856]  ffff800089277d00: f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 
> This issue seems to be related to the behavior of some gcc compilers and
> was also fixed on the s390 architecture before:
> 
>  commit d93a855c31b7 ("s390/ptrace: Avoid KASAN false positives in regs_get_kernel_stack_nth()")
> 
> As described in that commit, regs_get_kernel_stack_nth() has confirmed that
> `addr` is on the stack, so reading the value at `*addr` should be allowed.
> Use READ_ONCE_NOCHECK() helper to silence the KASAN check for this case.
> 
> Fixes: 0a8ea52c3eb1 ("arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature")
> Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
> ---
>  arch/arm64/kernel/ptrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index f79b0d5f71ac..fe3f7e554d14 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -141,7 +141,7 @@ unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
>  
>  	addr += n;
>  	if (regs_within_kernel_stack(regs, (unsigned long)addr))
> -		return *addr;
> +		return READ_ONCE_NOCHECK(addr);
>  	else
>  		return 0;
>  }