On 2020-07-10 3:04 p.m., Matthew Wilcox wrote:

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On Fri, Jul 10, 2020 at 02:00:32PM -0700, Scott Branden wrote:

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@@ -950,8 +951,8 @@ int kernel_read_file(struct file *file, void **buf, loff_t *size,
   		goto out;
   	}
-	if (id != READING_FIRMWARE_PREALLOC_BUFFER)
-		*buf = vmalloc(i_size);
+	if (!*buf)

The assumption that *buf is always NULL when id !=
READING_FIRMWARE_PREALLOC_BUFFER doesn't appear to be correct.
I get unhandled page faults due to this change on boot.

Did it give you a stack backtrace?

Yes, but there's no requirement that *buf need to be NULL when calling this
function.
To fix my particular crash I added the following locally:

--- a/kernel/module.c
+++ b/kernel/module.c

@@ -3989,7 +3989,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char

__user *, uargs, int, flags)
 {
     struct load_info info = { };
     loff_t size;
-    void *hdr;
+    void *hdr = NULL;
     int err;

     err = may_init_module();

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