arm64: compat: Alloc separate pages for vectors and sigpage

For AArch32 tasks, we install a special "[vectors]" page that contains
the sigreturn trampolines and kuser helpers, which is mapped at a fixed
address specified by the kuser helpers ABI.

Having the sigreturn trampolines in the same page as the kuser helpers
makes it impossible to disable the kuser helpers independently.

Follow the Arm implementation, by moving the signal trampolines out of
the "[vectors]" page and into their own "[sigpage]".

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[will: tweaked comments and fixed sparse warning]
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/elf.h

@@ -214,10 +214,10 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
 	set_thread_flag(TIF_32BIT);					\
  })
 #define COMPAT_ARCH_DLINFO
-extern int aarch32_setup_vectors_page(struct linux_binprm *bprm,
-				      int uses_interp);
+extern int aarch32_setup_additional_pages(struct linux_binprm *bprm,
+					  int uses_interp);
 #define compat_arch_setup_additional_pages \
-					aarch32_setup_vectors_page
+					aarch32_setup_additional_pages
 
 #endif /* CONFIG_COMPAT */
 

arch/arm64/include/asm/signal32.h

@@ -20,8 +20,6 @@
 #ifdef CONFIG_COMPAT
 #include <linux/compat.h>
 
-#define AARCH32_KERN_SIGRET_CODE_OFFSET	0x500
-
 int compat_setup_frame(int usig, struct ksignal *ksig, sigset_t *set,
 		       struct pt_regs *regs);
 int compat_setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,

arch/arm64/kernel/signal32.c

@@ -403,8 +403,7 @@ static void compat_setup_return(struct pt_regs *regs, struct k_sigaction *ka,
 		if (ka->sa.sa_flags & SA_SIGINFO)
 			idx += 3;
 
-		retcode = AARCH32_VECTORS_BASE +
-			  AARCH32_KERN_SIGRET_CODE_OFFSET +
+		retcode = (unsigned long)current->mm->context.vdso +
 			  (idx << 2) + thumb;
 	}
 

arch/arm64/kernel/vdso.c

 /*
- * VDSO implementation for AArch64 and vector page setup for AArch32.
+ * VDSO implementations.
  *
  * Copyright (C) 2012 ARM Limited
  *
@@ -53,61 +53,123 @@ struct vdso_data *vdso_data = &vdso_data_store.data;
 /*
  * Create and map the vectors page for AArch32 tasks.
  */
-static struct page *vectors_page[1] __ro_after_init;
+#define C_VECTORS	0
+#define C_SIGPAGE	1
+#define C_PAGES		(C_SIGPAGE + 1)
+static struct page *aarch32_vdso_pages[C_PAGES] __ro_after_init;
+static const struct vm_special_mapping aarch32_vdso_spec[C_PAGES] = {
+	{
+		.name	= "[vectors]", /* ABI */
+		.pages	= &aarch32_vdso_pages[C_VECTORS],
+	},
+	{
+		.name	= "[sigpage]", /* ABI */
+		.pages	= &aarch32_vdso_pages[C_SIGPAGE],
+	},
+};
 
-static int __init alloc_vectors_page(void)
+static int __init aarch32_alloc_vdso_pages(void)
 {
 	extern char __kuser_helper_start[], __kuser_helper_end[];
 	extern char __aarch32_sigret_code_start[], __aarch32_sigret_code_end[];
 
 	int kuser_sz = __kuser_helper_end - __kuser_helper_start;
 	int sigret_sz = __aarch32_sigret_code_end - __aarch32_sigret_code_start;
-	unsigned long vpage;
+	unsigned long vdso_pages[C_PAGES];
 
-	vpage = get_zeroed_page(GFP_ATOMIC);
+	vdso_pages[C_VECTORS] = get_zeroed_page(GFP_ATOMIC);
+	if (!vdso_pages[C_VECTORS])
+		return -ENOMEM;
 
-	if (!vpage)
+	vdso_pages[C_SIGPAGE] = get_zeroed_page(GFP_ATOMIC);
+	if (!vdso_pages[C_SIGPAGE]) {
+		free_page(vdso_pages[C_VECTORS]);
 		return -ENOMEM;
+	}
 
 	/* kuser helpers */
-	memcpy((void *)vpage + 0x1000 - kuser_sz, __kuser_helper_start,
-		kuser_sz);
+	memcpy((void *)(vdso_pages[C_VECTORS] + 0x1000 - kuser_sz),
+	       __kuser_helper_start,
+	       kuser_sz);
 
 	/* sigreturn code */
-	memcpy((void *)vpage + AARCH32_KERN_SIGRET_CODE_OFFSET,
-               __aarch32_sigret_code_start, sigret_sz);
+	memcpy((void *)vdso_pages[C_SIGPAGE], __aarch32_sigret_code_start,
+	       sigret_sz);
+
+	flush_icache_range(vdso_pages[C_VECTORS],
+			   vdso_pages[C_VECTORS] + PAGE_SIZE);
+	flush_icache_range(vdso_pages[C_SIGPAGE],
+			   vdso_pages[C_SIGPAGE] + PAGE_SIZE);
 
-	flush_icache_range(vpage, vpage + PAGE_SIZE);
-	vectors_page[0] = virt_to_page(vpage);
+	aarch32_vdso_pages[C_VECTORS] = virt_to_page(vdso_pages[C_VECTORS]);
+	aarch32_vdso_pages[C_SIGPAGE] = virt_to_page(vdso_pages[C_SIGPAGE]);
 
 	return 0;
 }
-arch_initcall(alloc_vectors_page);
+arch_initcall(aarch32_alloc_vdso_pages);
 
-int aarch32_setup_vectors_page(struct linux_binprm *bprm, int uses_interp)
+static int aarch32_kuser_helpers_setup(struct mm_struct *mm)
 {
-	struct mm_struct *mm = current->mm;
-	unsigned long addr = AARCH32_VECTORS_BASE;
-	static const struct vm_special_mapping spec = {
-		.name	= "[vectors]",
-		.pages	= vectors_page,
+	void *ret;
+
+	/*
+	 * Avoid VM_MAYWRITE for compatibility with arch/arm/, where it's
+	 * not safe to CoW the page containing the CPU exception vectors.
+	 */
+	ret = _install_special_mapping(mm, AARCH32_VECTORS_BASE, PAGE_SIZE,
+				       VM_READ | VM_EXEC |
+				       VM_MAYREAD | VM_MAYEXEC,
+				       &aarch32_vdso_spec[C_VECTORS]);
+
+	return PTR_ERR_OR_ZERO(ret);
+}
 
-	};
+static int aarch32_sigreturn_setup(struct mm_struct *mm)
+{
+	unsigned long addr;
 	void *ret;
 
-	if (down_write_killable(&mm->mmap_sem))
-		return -EINTR;
-	current->mm->context.vdso = (void *)addr;
+	addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
+	if (IS_ERR_VALUE(addr)) {
+		ret = ERR_PTR(addr);
+		goto out;
+	}
 
-	/* Map vectors page at the high address. */
+	/*
+	 * VM_MAYWRITE is required to allow gdb to Copy-on-Write and
+	 * set breakpoints.
+	 */
 	ret = _install_special_mapping(mm, addr, PAGE_SIZE,
-				       VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYEXEC,
-				       &spec);
+				       VM_READ | VM_EXEC | VM_MAYREAD |
+				       VM_MAYWRITE | VM_MAYEXEC,
+				       &aarch32_vdso_spec[C_SIGPAGE]);
+	if (IS_ERR(ret))
+		goto out;
 
-	up_write(&mm->mmap_sem);
+	mm->context.vdso = (void *)addr;
 
+out:
 	return PTR_ERR_OR_ZERO(ret);
 }
+
+int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
+{
+	struct mm_struct *mm = current->mm;
+	int ret;
+
+	if (down_write_killable(&mm->mmap_sem))
+		return -EINTR;
+
+	ret = aarch32_kuser_helpers_setup(mm);
+	if (ret)
+		goto out;
+
+	ret = aarch32_sigreturn_setup(mm);
+
+out:
+	up_write(&mm->mmap_sem);
+	return ret;
+}
 #endif /* CONFIG_COMPAT */
 
 static int vdso_mremap(const struct vm_special_mapping *sm,