From 37d22a0d798b5c938b277d32cfd86dc231381342 Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Tue, 1 Mar 2016 02:37:59 +0000 Subject: [PATCH] MIPS: Sync icache & dcache in set_pte_at It's possible for pages to become visible prior to update_mmu_cache running if a thread within the same address space preempts the current thread or runs simultaneously on another CPU. That is, the following scenario is possible: CPU0 CPU1 write to page flush_dcache_page flush_icache_page set_pte_at map page update_mmu_cache If CPU1 maps the page in between CPU0's set_pte_at, which marks it valid & visible, and update_mmu_cache where the dcache flush occurs then CPU1s icache will fill from stale data (unless it fills from the dcache, in which case all is good, but most MIPS CPUs don't have this property). Commit 4d46a67a3eb8 ("MIPS: Fix race condition in lazy cache flushing.") attempted to fix that by performing the dcache flush in flush_icache_page such that it occurs before the set_pte_at call makes the page visible. However it has the problem that not all code that writes to pages exposed to userland call flush_icache_page. There are many callers of set_pte_at under mm/ and only 2 of them do call flush_icache_page. Thus the race window between a page becoming visible & being coherent between the icache & dcache remains open in some cases. To illustrate some of the cases, a WARN was added to __update_cache with this patch applied that triggered in cases where a page about to be flushed from the dcache was not the last page provided to flush_icache_page. That is, backtraces were obtained for cases in which the race window is left open without this patch. The 2 standout examples follow. When forking a process: [ 15.271842] [<80417630>] __update_cache+0xcc/0x188 [ 15.277274] [<80530394>] copy_page_range+0x56c/0x6ac [ 15.282861] [<8042936c>] copy_process.part.54+0xd40/0x17ac [ 15.289028] [<80429f80>] do_fork+0xe4/0x420 [ 15.293747] [<80413808>] handle_sys+0x128/0x14c When exec'ing an ELF binary: [ 14.445964] [<80417630>] __update_cache+0xcc/0x188 [ 14.451369] [<80538d88>] move_page_tables+0x414/0x498 [ 14.457075] [<8055d848>] setup_arg_pages+0x220/0x318 [ 14.462685] [<805b0f38>] load_elf_binary+0x530/0x12a0 [ 14.468374] [<8055ec3c>] search_binary_handler+0xbc/0x214 [ 14.474444] [<8055f6c0>] do_execveat_common+0x43c/0x67c [ 14.480324] [<8055f938>] do_execve+0x38/0x44 [ 14.485137] [<80413808>] handle_sys+0x128/0x14c These code paths write into a page, call flush_dcache_page then call set_pte_at without flush_icache_page inbetween. The end result is that the icache can become corrupted & userland processes may execute unexpected or invalid code, typically resulting in a reserved instruction exception, a trap or a segfault. Fix this race condition fully by performing any cache maintenance required to keep the icache & dcache in sync in set_pte_at, before the page is made valid. This has the added bonus of ensuring the cache maintenance always happens in one location, rather than being duplicated in flush_icache_page & update_mmu_cache. It also matches the way other architectures solve the same problem (see arm, ia64 & powerpc). Signed-off-by: Paul Burton Reported-by: Ionela Voinescu Cc: Lars Persson Fixes: 4d46a67a3eb8 ("MIPS: Fix race condition in lazy cache flushing.") Cc: Steven J. Hill Cc: David Daney Cc: Huacai Chen Cc: Aneesh Kumar K.V Cc: Andrew Morton Cc: Jerome Marchand Cc: Kirill A. Shutemov Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Cc: stable # v4.1+ Patchwork: https://patchwork.linux-mips.org/patch/12722/ Signed-off-by: Ralf Baechle --- arch/mips/include/asm/cacheflush.h | 6 ------ arch/mips/include/asm/pgtable.h | 26 +++++++++++++++++++++----- arch/mips/mm/cache.c | 19 +++---------------- 3 files changed, 24 insertions(+), 27 deletions(-) diff --git a/arch/mips/include/asm/cacheflush.h b/arch/mips/include/asm/cacheflush.h index 7e9f46818eba..34ed22ec6c33 100644 --- a/arch/mips/include/asm/cacheflush.h +++ b/arch/mips/include/asm/cacheflush.h @@ -51,7 +51,6 @@ extern void (*flush_cache_range)(struct vm_area_struct *vma, unsigned long start, unsigned long end); extern void (*flush_cache_page)(struct vm_area_struct *vma, unsigned long page, unsigned long pfn); extern void __flush_dcache_page(struct page *page); -extern void __flush_icache_page(struct vm_area_struct *vma, struct page *page); #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1 static inline void flush_dcache_page(struct page *page) @@ -77,11 +76,6 @@ static inline void flush_anon_page(struct vm_area_struct *vma, static inline void flush_icache_page(struct vm_area_struct *vma, struct page *page) { - if (!cpu_has_ic_fills_f_dc && (vma->vm_flags & VM_EXEC) && - Page_dcache_dirty(page)) { - __flush_icache_page(vma, page); - ClearPageDcacheDirty(page); - } } extern void (*flush_icache_range)(unsigned long start, unsigned long end); diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h index 75c29cff0f99..45de57651619 100644 --- a/arch/mips/include/asm/pgtable.h +++ b/arch/mips/include/asm/pgtable.h @@ -127,10 +127,14 @@ do { \ } \ } while(0) +static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pteval); + #if defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32) #define pte_none(pte) (!(((pte).pte_high) & ~_PAGE_GLOBAL)) #define pte_present(pte) ((pte).pte_low & _PAGE_PRESENT) +#define pte_no_exec(pte) ((pte).pte_low & _PAGE_NO_EXEC) static inline void set_pte(pte_t *ptep, pte_t pte) { @@ -148,7 +152,6 @@ static inline void set_pte(pte_t *ptep, pte_t pte) buddy->pte_high |= _PAGE_GLOBAL; } } -#define set_pte_at(mm, addr, ptep, pteval) set_pte(ptep, pteval) static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep) { @@ -166,6 +169,7 @@ static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *pt #define pte_none(pte) (!(pte_val(pte) & ~_PAGE_GLOBAL)) #define pte_present(pte) (pte_val(pte) & _PAGE_PRESENT) +#define pte_no_exec(pte) (pte_val(pte) & _PAGE_NO_EXEC) /* * Certain architectures need to do special things when pte's @@ -230,7 +234,6 @@ static inline void set_pte(pte_t *ptep, pte_t pteval) } #endif } -#define set_pte_at(mm, addr, ptep, pteval) set_pte(ptep, pteval) static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep) { @@ -246,6 +249,22 @@ static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *pt } #endif +static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pteval) +{ + extern void __update_cache(unsigned long address, pte_t pte); + + if (!pte_present(pteval)) + goto cache_sync_done; + + if (pte_present(*ptep) && (pte_pfn(*ptep) == pte_pfn(pteval))) + goto cache_sync_done; + + __update_cache(addr, pteval); +cache_sync_done: + set_pte(ptep, pteval); +} + /* * (pmds are folded into puds so this doesn't get actually called, * but the define is needed for a generic inline function.) @@ -442,15 +461,12 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot) extern void __update_tlb(struct vm_area_struct *vma, unsigned long address, pte_t pte); -extern void __update_cache(struct vm_area_struct *vma, unsigned long address, - pte_t pte); static inline void update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep) { pte_t pte = *ptep; __update_tlb(vma, address, pte); - __update_cache(vma, address, pte); } static inline void update_mmu_cache_pmd(struct vm_area_struct *vma, diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c index 8befa55234df..bf04c6c479a4 100644 --- a/arch/mips/mm/cache.c +++ b/arch/mips/mm/cache.c @@ -125,30 +125,17 @@ void __flush_anon_page(struct page *page, unsigned long vmaddr) EXPORT_SYMBOL(__flush_anon_page); -void __flush_icache_page(struct vm_area_struct *vma, struct page *page) -{ - unsigned long addr; - - if (PageHighMem(page)) - return; - - addr = (unsigned long) page_address(page); - flush_data_cache_page(addr); -} -EXPORT_SYMBOL_GPL(__flush_icache_page); - -void __update_cache(struct vm_area_struct *vma, unsigned long address, - pte_t pte) +void __update_cache(unsigned long address, pte_t pte) { struct page *page; unsigned long pfn, addr; - int exec = (vma->vm_flags & VM_EXEC) && !cpu_has_ic_fills_f_dc; + int exec = !pte_no_exec(pte) && !cpu_has_ic_fills_f_dc; pfn = pte_pfn(pte); if (unlikely(!pfn_valid(pfn))) return; page = pfn_to_page(pfn); - if (page_mapping(page) && Page_dcache_dirty(page)) { + if (Page_dcache_dirty(page)) { if (PageHighMem(page)) addr = (unsigned long)kmap_atomic(page); else -- 2.20.1