[PATCH] x86/mm: Do not split_large_page() for set_kernel_text_rw()
From: Song Liu
Date: Fri Aug 23 2019 - 01:24:01 EST
As 4k pages check was removed from cpa [1], set_kernel_text_rw() leads to
split_large_page() for all kernel text pages. This means a single kprobe
will put all kernel text in 4k pages:
root@ ~# grep ffff81000000- /sys/kernel/debug/page_tables/kernel
0xffffffff81000000-0xffffffff82400000 20M ro PSE x pmd
root@ ~# echo ONE_KPROBE >> /sys/kernel/debug/tracing/kprobe_events
root@ ~# echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
root@ ~# grep ffff81000000- /sys/kernel/debug/page_tables/kernel
0xffffffff81000000-0xffffffff82400000 20M ro x pte
To fix this issue, introduce CPA_FLIP_TEXT_RW to bypass "Text RO" check
in static_protections().
Two helper functions set_text_rw() and set_text_ro() are added to flip
_PAGE_RW bit for kernel text.
[1] commit 585948f4f695 ("x86/mm/cpa: Avoid the 4k pages check completely")
Fixes: 585948f4f695 ("x86/mm/cpa: Avoid the 4k pages check completely")
Cc: stable@xxxxxxxxxxxxxxx # v4.20+
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
arch/x86/mm/init_64.c | 4 ++--
arch/x86/mm/mm_internal.h | 4 ++++
arch/x86/mm/pageattr.c | 34 +++++++++++++++++++++++++---------
3 files changed, 31 insertions(+), 11 deletions(-)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a6b5c653727b..5745fdcc429e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1276,7 +1276,7 @@ void set_kernel_text_rw(void)
* mapping will always be RO. Refer to the comment in
* static_protections() in pageattr.c
*/
- set_memory_rw(start, (end - start) >> PAGE_SHIFT);
+ set_text_rw(start, (end - start) >> PAGE_SHIFT);
}
void set_kernel_text_ro(void)
@@ -1293,7 +1293,7 @@ void set_kernel_text_ro(void)
/*
* Set the kernel identity mapping for text RO.
*/
- set_memory_ro(start, (end - start) >> PAGE_SHIFT);
+ set_text_ro(start, (end - start) >> PAGE_SHIFT);
}
void mark_rodata_ro(void)
diff --git a/arch/x86/mm/mm_internal.h b/arch/x86/mm/mm_internal.h
index eeae142062ed..65b84b471770 100644
--- a/arch/x86/mm/mm_internal.h
+++ b/arch/x86/mm/mm_internal.h
@@ -24,4 +24,8 @@ void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);
extern unsigned long tlb_single_page_flush_ceiling;
+int set_text_rw(unsigned long addr, int numpages);
+
+int set_text_ro(unsigned long addr, int numpages);
+
#endif /* __X86_MM_INTERNAL_H */
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 6a9a77a403c9..44a885df776d 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -66,6 +66,7 @@ static DEFINE_SPINLOCK(cpa_lock);
#define CPA_ARRAY 2
#define CPA_PAGES_ARRAY 4
#define CPA_NO_CHECK_ALIAS 8 /* Do not search for aliases */
+#define CPA_FLIP_TEXT_RW 0x10 /* allow flip _PAGE_RW for kernel text */
#ifdef CONFIG_PROC_FS
static unsigned long direct_pages_count[PG_LEVEL_NUM];
@@ -516,7 +517,7 @@ static inline void check_conflict(int warnlvl, pgprot_t prot, pgprotval_t val,
*/
static inline pgprot_t static_protections(pgprot_t prot, unsigned long start,
unsigned long pfn, unsigned long npg,
- int warnlvl)
+ int warnlvl, unsigned int cpa_flags)
{
pgprotval_t forbidden, res;
unsigned long end;
@@ -535,9 +536,11 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long start,
check_conflict(warnlvl, prot, res, start, end, pfn, "Text NX");
forbidden = res;
- res = protect_kernel_text_ro(start, end);
- check_conflict(warnlvl, prot, res, start, end, pfn, "Text RO");
- forbidden |= res;
+ if (!(cpa_flags & CPA_FLIP_TEXT_RW)) {
+ res = protect_kernel_text_ro(start, end);
+ check_conflict(warnlvl, prot, res, start, end, pfn, "Text RO");
+ forbidden |= res;
+ }
/* Check the PFN directly */
res = protect_pci_bios(pfn, pfn + npg - 1);
@@ -819,7 +822,7 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
* extra conditional required here.
*/
chk_prot = static_protections(old_prot, lpaddr, old_pfn, numpages,
- CPA_CONFLICT);
+ CPA_CONFLICT, cpa->flags);
if (WARN_ON_ONCE(pgprot_val(chk_prot) != pgprot_val(old_prot))) {
/*
@@ -855,7 +858,7 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
* protection requirement in the large page.
*/
new_prot = static_protections(req_prot, lpaddr, old_pfn, numpages,
- CPA_DETECT);
+ CPA_DETECT, cpa->flags);
/*
* If there is a conflict, split the large page.
@@ -906,7 +909,7 @@ static void split_set_pte(struct cpa_data *cpa, pte_t *pte, unsigned long pfn,
if (!cpa->force_static_prot)
goto set;
- prot = static_protections(ref_prot, address, pfn, npg, CPA_PROTECT);
+ prot = static_protections(ref_prot, address, pfn, npg, CPA_PROTECT, 0);
if (pgprot_val(prot) == pgprot_val(ref_prot))
goto set;
@@ -1504,7 +1507,7 @@ static int __change_page_attr(struct cpa_data *cpa, int primary)
cpa_inc_4k_install();
new_prot = static_protections(new_prot, address, pfn, 1,
- CPA_PROTECT);
+ CPA_PROTECT, 0);
new_prot = pgprot_clear_protnone_bits(new_prot);
@@ -1707,7 +1710,7 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages,
cpa.curpage = 0;
cpa.force_split = force_split;
- if (in_flag & (CPA_ARRAY | CPA_PAGES_ARRAY))
+ if (in_flag & (CPA_ARRAY | CPA_PAGES_ARRAY | CPA_FLIP_TEXT_RW))
cpa.flags |= in_flag;
/* No alias checking for _NX bit modifications */
@@ -1983,11 +1986,24 @@ int set_memory_ro(unsigned long addr, int numpages)
return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW), 0);
}
+int set_text_ro(unsigned long addr, int numpages)
+{
+ return change_page_attr_set_clr(&addr, numpages, __pgprot(0),
+ __pgprot(_PAGE_RW), 0, CPA_FLIP_TEXT_RW,
+ NULL);
+}
+
int set_memory_rw(unsigned long addr, int numpages)
{
return change_page_attr_set(&addr, numpages, __pgprot(_PAGE_RW), 0);
}
+int set_text_rw(unsigned long addr, int numpages)
+{
+ return change_page_attr_set_clr(&addr, numpages, __pgprot(_PAGE_RW),
+ __pgprot(0), 0, CPA_FLIP_TEXT_RW, NULL);
+}
+
int set_memory_np(unsigned long addr, int numpages)
{
return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_PRESENT), 0);
--
2.17.1