Bug in patch "x86/pti: Add the pti= cmdline option and documentation"

Bug in patch "x86/pti: Add the pti= cmdline option and documentation"

[Juergen Gross]

The patch in the tip tree with commit 506bcdf68b07a0335751e1fe8be37
("x86/pti: Add the pti= cmdline option and documentation") is completely
wrong: cmdline_find_option() will return -1 in case the otion isn't
found and the len of the argument in case it has been found.


Juergen

Re: Bug in patch "x86/pti: Add the pti= cmdline option and documentation"

[Borislav Petkov]

On Fri, Dec 22, 2017 at 05:41:32PM +0100, Juergen Gross wrote:
> The patch in the tip tree with commit 506bcdf68b07a0335751e1fe8be37
> ("x86/pti: Add the pti= cmdline option and documentation") is completely
> wrong: cmdline_find_option() will return -1 in case the otion isn't
> found and the len of the argument in case it has been found.

It is not completely wrong - we still walk into the if-branch. Besides,
we moved the xen check upwards, before that so it is not relevant for
the xen case.

Regardless, I'll send a correction soon to check the retval directly.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

Re: Bug in patch "x86/pti: Add the pti= cmdline option and documentation"

[Thomas Gleixner]

On Fri, 22 Dec 2017, Juergen Gross wrote:

> The patch in the tip tree with commit 506bcdf68b07a0335751e1fe8be37
> ("x86/pti: Add the pti= cmdline option and documentation") is completely
> wrong: cmdline_find_option() will return -1 in case the otion isn't
> found and the len of the argument in case it has been found.

AArgh .....

Re: Bug in patch "x86/pti: Add the pti= cmdline option and documentation"

[Borislav Petkov]

On Fri, Dec 22, 2017 at 05:43:50PM +0100, Thomas Gleixner wrote:
> On Fri, 22 Dec 2017, Juergen Gross wrote:
> 
> > The patch in the tip tree with commit 506bcdf68b07a0335751e1fe8be37
> > ("x86/pti: Add the pti= cmdline option and documentation") is completely
> > wrong: cmdline_find_option() will return -1 in case the otion isn't
> > found and the len of the argument in case it has been found.
> 
> AArgh .....

Please fold this in:

---
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 2a5c1b9bdf73..f9fd4eb74d20 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -69,13 +69,15 @@ static void __init pti_print_if_secure(const char *reason)
 void __init pti_check_boottime_disable(void)
 {
 	char arg[5];
+	int ret;
 
 	if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
 		pti_print_if_insecure("disabled on XEN PV.");
 		return;
 	}
 
-	if (cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg))) {
+	ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
+	if (ret > 0)  {
 		if (!strncmp(arg, "off", 3)) {
 			pti_print_if_insecure("disabled on command line.");
 			return;

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--