6.6-stable review patch. If anyone has any objections, please let me know.
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From: Zhichi Lin zhichi.lin@vivo.com
commit 08bd4c46d5e63b78e77f2605283874bbe868ab19 upstream.
__scs_magic() needs a 'void *' variable, but a 'struct task_struct *' is given. 'task_scs(tsk)' is the starting address of the task's shadow call stack, and '__scs_magic(task_scs(tsk))' is the end address of the task's shadow call stack. Here should be '__scs_magic(task_scs(tsk))'.
The user-visible effect of this bug is that when CONFIG_DEBUG_STACK_USAGE is enabled, the shadow call stack usage checking function (scs_check_usage) would scan an incorrect memory range. This could lead to:
1. **Inaccurate stack usage reporting**: The function would calculate wrong usage statistics for the shadow call stack, potentially showing incorrect value in kmsg.
2. **Potential kernel crash**: If the value of __scs_magic(tsk)is greater than that of __scs_magic(task_scs(tsk)), the for loop may access unmapped memory, potentially causing a kernel panic. However, this scenario is unlikely because task_struct is allocated via the slab allocator (which typically returns lower addresses), while the shadow call stack returned by task_scs(tsk) is allocated via vmalloc(which typically returns higher addresses).
However, since this is purely a debugging feature (CONFIG_DEBUG_STACK_USAGE), normal production systems should be not unaffected. The bug only impacts developers and testers who are actively debugging stack usage with this configuration enabled.
Link: https://lkml.kernel.org/r/20251011082222.12965-1-zhichi.lin@vivo.com Fixes: 5bbaf9d1fcb9 ("scs: Add support for stack usage debugging") Signed-off-by: Jiyuan Xie xiejiyuan@vivo.com Signed-off-by: Zhichi Lin zhichi.lin@vivo.com Reviewed-by: Sami Tolvanen samitolvanen@google.com Acked-by: Will Deacon will@kernel.org Cc: Andrey Konovalov andreyknvl@gmail.com Cc: Kees Cook keescook@chromium.org Cc: Marco Elver elver@google.com Cc: Will Deacon will@kernel.org Cc: Yee Lee yee.lee@mediatek.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/scs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/scs.c +++ b/kernel/scs.c @@ -135,7 +135,7 @@ static void scs_check_usage(struct task_ if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE)) return;
- for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) { + for (p = task_scs(tsk); p < __scs_magic(task_scs(tsk)); ++p) { if (!READ_ONCE_NOCHECK(*p)) break; used += sizeof(*p);