x86/criu: shstk: restore SHSTK via premap loops

* call shstk_vma_restore() for VMA_AREA_SHSTK in both premap loops
* delete map/copy/unmap from shstk_restore() and keep token setup + finalize
* before the loop naturally stopped at cet->ssp-8, so a -8 nudge is required here

Signed-off-by: Igor Svilenkov Bozic <svilenkov@gmail.com>
Co-Authored-By: Andrei Vagin <avagin@gmail.com>

Author: 2 people

criu/arch/x86/include/asm/shstk.h

@@ -201,28 +201,11 @@ static always_inline int shstk_vma_restore(unsigned long *shstk_data, unsigned l
  */
 static always_inline int shstk_restore(struct rst_shstk_info *cet)
 {
-	unsigned long *shstk_data = (unsigned long *)cet->premmaped_addr;
-	unsigned long ssp = cet->vma_start + cet->vma_size - 8;
-	unsigned long shstk_top = cet->vma_size / 8 - 1;
-	unsigned long val;
-	long ret;
+	unsigned long ssp, val;
 
 	if (!(cet->cet & ARCH_SHSTK_SHSTK))
 		return 0;
 
-	if (shstk_map(cet->vma_start, cet->vma_size))
-		return -1;
-
-	/*
-	 * Switch shadow stack from temporary location to the actual task's
-	 * shadow stack VMA
-	 */
-	shstk_switch_ssp(ssp);
-
-	/* restore shadow stack contents */
-	for (; ssp >= cet->ssp; ssp -= 8, shstk_top--)
-		wrssq(ssp, shstk_data[shstk_top]);
-
 	/*
 	 * Add tokens for sigreturn frame and for switch of the shadow stack.
 	 * The sigreturn token will be checked by the kernel during
@@ -232,6 +215,7 @@ static always_inline int shstk_restore(struct rst_shstk_info *cet)
 	 */
 
 	/* token for sigreturn frame */
+	ssp = cet->ssp - 8;
 	val = ALIGN_DOWN(cet->ssp, 8) | SHSTK_DATA_BIT;
 	wrssq(ssp, val);
 
@@ -243,12 +227,6 @@ static always_inline int shstk_restore(struct rst_shstk_info *cet)
 	/* reset shadow stack pointer to the proper location */
 	shstk_switch_ssp(ssp);
 
-	ret = sys_munmap(shstk_data, cet->vma_size + PAGE_SIZE);
-	if (ret < 0) {
-		pr_err("Failed to unmap premmaped shadow stack\n");
-		return ret;
-	}
-
 	return shstk_finalize();
 }
 #define arch_shstk_restore shstk_restore

criu/pie/restorer.c

@@ -1811,12 +1811,11 @@ __visible long __export_restore_task(struct task_restore_args *args)
 		if (vma_entry->start > vma_entry->shmid)
 			break;
 
-		/*
-		 * shadow stack VMAs cannot be remapped, they must be
-		 * recreated with map_shadow_stack system call
-		 */
-		if (vma_entry_is(vma_entry, VMA_AREA_SHSTK))
+		if (vma_entry_is(vma_entry, VMA_AREA_SHSTK)) {
+			if (shstk_vma_restore((void *)vma_premmaped_start(vma_entry), vma_entry->start, vma_entry_len(vma_entry)))
+				goto core_restore_end;
 			continue;
+		}
 
 		if (vma_remap(vma_entry, args->uffd))
 			goto core_restore_end;
@@ -1835,12 +1834,11 @@ __visible long __export_restore_task(struct task_restore_args *args)
 		if (vma_entry->start < vma_entry->shmid)
 			break;
 
-		/*
-		 * shadow stack VMAs cannot be remapped, they must be
-		 * recreated with map_shadow_stack system call
-		 */
-		if (vma_entry_is(vma_entry, VMA_AREA_SHSTK))
+		if (vma_entry_is(vma_entry, VMA_AREA_SHSTK)) {
+			if (shstk_vma_restore((void *)vma_premmaped_start(vma_entry), vma_entry->start, vma_entry_len(vma_entry)))
+				goto core_restore_end;
 			continue;
+		}
 
 		if (vma_remap(vma_entry, args->uffd))
 			goto core_restore_end;