Commit 502f6604 authored by Suresh Siddha's avatar Suresh Siddha Committed by Ingo Molnar
Browse files

x86, cpa: Fix kernel text RO checks in static_protection() 



Steven Rostedt reported that we are unconditionally making the
kernel text mapping as read-only. i.e., if someone does cpa() to
the kernel text area for setting/clearing any page table
attribute, we unconditionally clear the read-write attribute for
the kernel text mapping that is set at compile time.

We should delay (to forbid the write attribute) and enforce only
after the kernel has mapped the text as read-only.

Reported-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Tested-by: default avatarSteven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20091029024820.996634347@sbs-t61.sc.intel.com>
[ marked kernel_set_to_readonly as __read_mostly ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 883242dd

arch/x86/include/asm/cacheflush.h

+1 −0
Original line number Diff line number Diff line
@@ -176,6 +176,7 @@ void clflush_cache_range(void *addr, unsigned int size); 
#ifdef CONFIG_DEBUG_RODATA

void mark_rodata_ro(void);

extern const int rodata_test_data;

extern int kernel_set_to_readonly;

void set_kernel_text_rw(void);

void set_kernel_text_ro(void);

#else

arch/x86/mm/init_32.c

+1 −1
Original line number Diff line number Diff line
@@ -997,7 +997,7 @@ static noinline int do_test_wp_bit(void) 
const int rodata_test_data = 0xC3;

EXPORT_SYMBOL_GPL(rodata_test_data);



static int kernel_set_to_readonly;

int kernel_set_to_readonly __read_mostly;



void set_kernel_text_rw(void)

{

arch/x86/mm/init_64.c

+1 −1
Original line number Diff line number Diff line
@@ -695,7 +695,7 @@ void __init mem_init(void) 
const int rodata_test_data = 0xC3;

EXPORT_SYMBOL_GPL(rodata_test_data);



static int kernel_set_to_readonly;

int kernel_set_to_readonly;



void set_kernel_text_rw(void)

{

arch/x86/mm/pageattr.c

+6 −4
Original line number Diff line number Diff line
@@ -282,14 +282,16 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address, 
#if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA) && \

	!defined(CONFIG_DYNAMIC_FTRACE)

	/*

	 * Kernel text mappings for the large page aligned .rodata section

	 * will be read-only. For the kernel identity mappings covering

	 * the holes caused by this alignment can be anything.

	 * Once the kernel maps the text as RO (kernel_set_to_readonly is set),

	 * kernel text mappings for the large page aligned text, rodata sections

	 * will be always read-only. For the kernel identity mappings covering

	 * the holes caused by this alignment can be anything that user asks.

	 *

	 * This will preserve the large page mappings for kernel text/data

	 * at no extra cost.

	 */

	if (within(address, (unsigned long)_text,

	if (kernel_set_to_readonly &&

	    within(address, (unsigned long)_text,

		   (unsigned long)__end_rodata_hpage_align))

		pgprot_val(forbidden) |= _PAGE_RW;

#endif

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