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@vger.kernel.org # v4.20+ Cc: Thomas Gleixner tglx@linutronix.de Cc: Dave Hansen dave.hansen@intel.com Cc: Peter Zijlstra peterz@infradead.org Signed-off-by: Song Liu songliubraving@fb.com --- 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);