From: Rick Edgecombe Date: Fri, 8 Sep 2023 20:36:55 +0000 (-0700) Subject: x86/shstk: Add warning for shadow stack double unmap X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=509ff51ee652c41a277c2b439aea01a8f56a27b9;p=linux.git x86/shstk: Add warning for shadow stack double unmap There are several ways a thread's shadow stacks can get unmapped. This can happen on exit or exec, as well as error handling in exec or clone. The task struct already keeps track of the thread's shadow stack. Use the size variable to keep track of if the shadow stack has already been freed. When an attempt to double unmap the thread shadow stack is caught, warn about it and abort the operation. Signed-off-by: Rick Edgecombe Signed-off-by: Dave Hansen Tested-by: H.J. Lu Link: https://lore.kernel.org/all/20230908203655.543765-4-rick.p.edgecombe%40intel.com --- diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c index ad63252ebebcd..59e15dd8d0f86 100644 --- a/arch/x86/kernel/shstk.c +++ b/arch/x86/kernel/shstk.c @@ -426,7 +426,18 @@ void shstk_free(struct task_struct *tsk) if (!shstk->base) return; + /* + * shstk->base is NULL for CLONE_VFORK child tasks, and so is + * normal. But size = 0 on a shstk->base is not normal and + * indicated an attempt to free the thread shadow stack twice. + * Warn about it. + */ + if (WARN_ON(!shstk->size)) + return; + unmap_shadow_stack(shstk->base, shstk->size); + + shstk->size = 0; } static int wrss_control(bool enable)