mm/core: Do not enforce PKEY permissions on remote mm access

We try to enforce protection keys in software the same way that we
do in hardware.  (See long example below).

But, we only want to do this when accessing our *own* process's
memory.  If GDB set PKRU[6].AD=1 (disable access to PKEY 6), then
tried to PTRACE_POKE a target process which just happened to have
some mprotect_pkey(pkey=6) memory, we do *not* want to deny the
debugger access to that memory.  PKRU is fundamentally a
thread-local structure and we do not want to enforce it on access
to _another_ thread's data.

This gets especially tricky when we have workqueues or other
delayed-work mechanisms that might run in a random process's context.
We can check that we only enforce pkeys when operating on our *own* mm,
but delayed work gets performed when a random user context is active.
We might end up with a situation where a delayed-work gup fails when
running randomly under its "own" task but succeeds when running under
another process.  We want to avoid that.

To avoid that, we use the new GUP flag: FOLL_REMOTE and add a
fault flag: FAULT_FLAG_REMOTE.  They indicate that we are
walking an mm which is not guranteed to be the same as
current->mm and should not be subject to protection key
enforcement.

Thanks to Jerome Glisse for pointing out this scenario.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dominik Dingel <dingel@linux.vnet.ibm.com>
Cc: Dominik Vogt <vogt@linux.vnet.ibm.com>
Cc: Eric B Munson <emunson@akamai.com>
Cc: Geliang Tang <geliangtang@163.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Low <jason.low2@hp.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Shachar Raindel <raindel@mellanox.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xie XiuQi <xiexiuqi@huawei.com>
Cc: iommu@lists.linux-foundation.org
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-s390@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index a0f1838c8e78e409f9b5ae04d7bc93b254ef44d6..df9bf3ed025b408a85385a406e335a8c51878a90 100644 (file)
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -148,7 +148,8 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
 {
 }
 
-static inline bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write)
+static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
+               bool write, bool foreign)
 {
        /* by default, allow everything */
        return true;

diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 2627b338382cd448755c107d8d34d1c6dff28ce3..8906600922ce916add497a7cf659c987d29e7364 100644 (file)
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -130,7 +130,8 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
 {
 }
 
-static inline bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write)
+static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
+               bool write, bool foreign)
 {
        /* by default, allow everything */
        return true;

diff --git a/arch/unicore32/include/asm/mmu_context.h b/arch/unicore32/include/asm/mmu_context.h
index 3133f947ade27338abda2246910fe3458d43bb44..e35632ef23c759a43e4673d222aac430172cdad7 100644 (file)
--- a/arch/unicore32/include/asm/mmu_context.h
+++ b/arch/unicore32/include/asm/mmu_context.h
@@ -97,7 +97,8 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
 {
 }
 
-static inline bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write)
+static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
+               bool write, bool foreign)
 {
        /* by default, allow everything */
        return true;

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 19036cdbed8ffbda1141c53d31ef18a47014af8b..b4d939a17e609ec771f5579c9b7350f68e8cb0f6 100644 (file)
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -322,10 +322,11 @@ static inline bool vma_is_foreign(struct vm_area_struct *vma)
        return false;
 }
 
-static inline bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write)
+static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
+               bool write, bool foreign)
 {
        /* allow access if the VMA is not one from this process */
-       if (vma_is_foreign(vma))
+       if (foreign || vma_is_foreign(vma))
                return true;
        return __pkru_allows_pkey(vma_pkey(vma), write);
 }

diff --git a/drivers/iommu/amd_iommu_v2.c b/drivers/iommu/amd_iommu_v2.c
index c865737326e1a17e9f6d542387175e0d324fe06e..56999d2fac070483dc72ce662e32567fb63ebb09 100644 (file)
--- a/drivers/iommu/amd_iommu_v2.c
+++ b/drivers/iommu/amd_iommu_v2.c
@@ -526,6 +526,7 @@ static void do_fault(struct work_struct *work)
                flags |= FAULT_FLAG_USER;
        if (fault->flags & PPR_FAULT_WRITE)
                flags |= FAULT_FLAG_WRITE;
+       flags |= FAULT_FLAG_REMOTE;
 
        down_read(&mm->mmap_sem);
        vma = find_extend_vma(mm, address);

diff --git a/include/asm-generic/mm_hooks.h b/include/asm-generic/mm_hooks.h
index c1fc5af3c3843f24982c7d9913ccdf9da0ba92bb..d5c9633bd9558acece222238299e9c7fcb34e7d3 100644 (file)
--- a/include/asm-generic/mm_hooks.h
+++ b/include/asm-generic/mm_hooks.h
@@ -26,7 +26,8 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
 {
 }
 
-static inline bool arch_vma_access_permitted(struct vm_area_struct *vma, bool write)
+static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
+               bool write, bool foreign)
 {
        /* by default, allow everything */
        return true;

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3056369bab1d766a8a5e1b5b72f12fb58e9d2a53..2aaa0f0d67ea07559d4de6a3899639a0c7adf539 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -251,6 +251,7 @@ extern pgprot_t protection_map[16];
 #define FAULT_FLAG_KILLABLE    0x10    /* The fault task is in SIGKILL killable region */
 #define FAULT_FLAG_TRIED       0x20    /* Second try */
 #define FAULT_FLAG_USER                0x40    /* The fault originated in userspace */
+#define FAULT_FLAG_REMOTE      0x80    /* faulting for non current tsk/mm */
 
 /*
  * vm_fault is filled by the the pagefault handler and passed to the vma's

diff --git a/mm/gup.c b/mm/gup.c
index e0f5f3574d16a9749efff3fc53d502e5f1614453..d276760163b3384c8d54d65c1ed81caa46c4931d 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -365,6 +365,8 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
                return -ENOENT;
        if (*flags & FOLL_WRITE)
                fault_flags |= FAULT_FLAG_WRITE;
+       if (*flags & FOLL_REMOTE)
+               fault_flags |= FAULT_FLAG_REMOTE;
        if (nonblocking)
                fault_flags |= FAULT_FLAG_ALLOW_RETRY;
        if (*flags & FOLL_NOWAIT)
@@ -415,11 +417,13 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 {
        vm_flags_t vm_flags = vma->vm_flags;
+       int write = (gup_flags & FOLL_WRITE);
+       int foreign = (gup_flags & FOLL_REMOTE);
 
        if (vm_flags & (VM_IO | VM_PFNMAP))
                return -EFAULT;
 
-       if (gup_flags & FOLL_WRITE) {
+       if (write) {
                if (!(vm_flags & VM_WRITE)) {
                        if (!(gup_flags & FOLL_FORCE))
                                return -EFAULT;
@@ -445,7 +449,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
                if (!(vm_flags & VM_MAYREAD))
                        return -EFAULT;
        }
-       if (!arch_vma_access_permitted(vma, (gup_flags & FOLL_WRITE)))
+       if (!arch_vma_access_permitted(vma, write, foreign))
                return -EFAULT;
        return 0;
 }
@@ -615,7 +619,8 @@ EXPORT_SYMBOL(__get_user_pages);
 
 bool vma_permits_fault(struct vm_area_struct *vma, unsigned int fault_flags)
 {
-       bool write = !!(fault_flags & FAULT_FLAG_WRITE);
+       bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
+       bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
        vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
 
        if (!(vm_flags & vma->vm_flags))
@@ -623,9 +628,9 @@ bool vma_permits_fault(struct vm_area_struct *vma, unsigned int fault_flags)
 
        /*
         * The architecture might have a hardware protection
-        * mechanism other than read/write that can deny access
+        * mechanism other than read/write that can deny access.
         */
-       if (!arch_vma_access_permitted(vma, write))
+       if (!arch_vma_access_permitted(vma, write, foreign))
                return false;
 
        return true;

diff --git a/mm/ksm.c b/mm/ksm.c
index c2013f638d113d073d0ca2814420619472c63915..b99e828172f6ef30e279e4d07b7a74ba9cbb36db 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -359,6 +359,10 @@ static inline bool ksm_test_exit(struct mm_struct *mm)
  * in case the application has unmapped and remapped mm,addr meanwhile.
  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
+ *
+ * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
+ * of the process that owns 'vma'.  We also do not want to enforce
+ * protection keys here anyway.
  */
 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 {
@@ -367,12 +371,14 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 
        do {
                cond_resched();
-               page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION);
+               page = follow_page(vma, addr,
+                               FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
                if (IS_ERR_OR_NULL(page))
                        break;
                if (PageKsm(page))
                        ret = handle_mm_fault(vma->vm_mm, vma, addr,
-                                                       FAULT_FLAG_WRITE);
+                                                       FAULT_FLAG_WRITE |
+                                                       FAULT_FLAG_REMOTE);
                else
                        ret = VM_FAULT_WRITE;
                put_page(page);

diff --git a/mm/memory.c b/mm/memory.c
index d7e84fe6504dd622cc87babd30ba27cc3ec712da..76c44e5dffa2b6c0a157f4af6e640323084a7388 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3379,7 +3379,8 @@ static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
        pmd_t *pmd;
        pte_t *pte;
 
-       if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE))
+       if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+                                           flags & FAULT_FLAG_REMOTE))
                return VM_FAULT_SIGSEGV;
 
        if (unlikely(is_vm_hugetlb_page(vma)))