[PATCH 2/9] x86/mm: don't set kernel_set_to_readonly when write protecting fails

["Mike Rapoport (Microsoft)" <rppt@kernel.org>]

mark_rodata_ro() ignores the result of write protecting the kernel text
and rodata. It can fail when CPA cannot allocate a page table to split a
large page, and then a part of the text and rodata stays writable.

kernel_set_to_readonly is set anyway, and CPA enforces the static
protections of rodata from then on. On 64-bit the next call,
set_memory_nx() for the data, may find the writable rodata and warn
about a conflict with the static protections, which does not say what
actually went wrong.

Report the failure and set kernel_set_to_readonly only when write
protecting succeeds.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 arch/x86/mm/init_32.c | 8 ++++++--
 arch/x86/mm/init_64.c | 8 ++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 0908c44d51e6f..8323c1f599f25 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -741,12 +741,16 @@ void mark_rodata_ro(void)
 {
 	unsigned long start = PFN_ALIGN(_text);
 	unsigned long size = (unsigned long)__end_rodata - start;
+	int err;
 
-	set_pages_ro(virt_to_page(start), size >> PAGE_SHIFT);
+	err = set_pages_ro(virt_to_page(start), size >> PAGE_SHIFT);
 	pr_info("Write protecting kernel text and read-only data: %luk\n",
 		size >> 10);
+	if (err)
+		pr_err("Failed to write protect kernel text and read-only data: %d\n",
+		       err);
 
-	kernel_set_to_readonly = 1;
+	kernel_set_to_readonly = !err;
 
 #ifdef CONFIG_CPA_DEBUG
 	pr_info("Testing CPA: Reverting %lx-%lx\n", start, start + size);
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 8b6d86fb5a42e..a68998f359bf3 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1365,12 +1365,16 @@ void mark_rodata_ro(void)
 	unsigned long text_end = PFN_ALIGN(_etext);
 	unsigned long rodata_end = PFN_ALIGN(__end_rodata);
 	unsigned long all_end;
+	int err;
 
 	printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
 	       (end - start) >> 10);
-	set_memory_ro(start, (end - start) >> PAGE_SHIFT);
+	err = set_memory_ro(start, (end - start) >> PAGE_SHIFT);
+	if (err)
+		pr_err("Failed to write protect the kernel read-only data: %d\n",
+		       err);
 
-	kernel_set_to_readonly = 1;
+	kernel_set_to_readonly = !err;
 
 	/*
 	 * The rodata/data/bss/brk section (but not the kernel text!)

-- 
2.53.0