Commit 952a6c2c authored Mar 30, 2017 by Borislav Petkov Committed by Ingo Molnar Mar 31, 2017

x86/boot/32: Flip the logic in test_wp_bit()



... to have a natural "likely()" in the code flow and thus have the
success case with a branch 99.999% of the times non-taken and function
return code following it instead of jumping to it each time.

This puts the panic() call at the end of the function - it is going to
be practically unreachable anyway.

The C code is a bit more readable too.

No functionality change.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: thgarnie@google.com
Link: http://lkml.kernel.org/r/20170330080101.ywsf5rg6ilzu4itk@pd.tnic


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4af17110

arch/x86/mm/init_32.c

+7 −8

Original line number	Diff line number	Diff line
		@@ -726,19 +726,18 @@ static void __init test_wp_bit(void)
		{
		char z = 0;

		printk(KERN_INFO
		"Checking if this processor honours the WP bit even in supervisor mode...");
		printk(KERN_INFO "Checking if this processor honours the WP bit even in supervisor mode...");

		__set_fixmap(FIX_WP_TEST, __pa_symbol(empty_zero_page), PAGE_KERNEL_RO);

		if (probe_kernel_write((char *)fix_to_virt(FIX_WP_TEST), &z, 1) == 0) {
		printk(KERN_CONT "No.\n");
		panic("Linux doesn't support CPUs with broken WP.");
		}

		if (probe_kernel_write((char *)fix_to_virt(FIX_WP_TEST), &z, 1)) {
		clear_fixmap(FIX_WP_TEST);

		printk(KERN_CONT "Ok.\n");
		return;
		}

		printk(KERN_CONT "No.\n");
		panic("Linux doesn't support CPUs with broken WP.");
		}

		void __init mem_init(void)

Admin message