From: "tip-bot for Kirill A. Shutemov" <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
tglx@linutronix.de, kirill.shutemov@linux.intel.com
Subject: [tip:x86/urgent] x86/ldt: Unmap PTEs for the slot before freeing LDT pages
Date: Tue, 6 Nov 2018 12:40:25 -0800 [thread overview]
Message-ID: <tip-a0e6e0831c516860fc7f9be1db6c081fe902ebcf@git.kernel.org> (raw)
In-Reply-To: <20181026122856.66224-3-kirill.shutemov@linux.intel.com>
Commit-ID: a0e6e0831c516860fc7f9be1db6c081fe902ebcf
Gitweb: https://git.kernel.org/tip/a0e6e0831c516860fc7f9be1db6c081fe902ebcf
Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
AuthorDate: Fri, 26 Oct 2018 15:28:55 +0300
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 6 Nov 2018 21:35:11 +0100
x86/ldt: Unmap PTEs for the slot before freeing LDT pages
modify_ldt(2) leaves the old LDT mapped after switching over to the new
one. The old LDT gets freed and the pages can be re-used.
Leaving the mapping in place can have security implications. The mapping is
present in the userspace page tables and Meltdown-like attacks can read
these freed and possibly reused pages.
It's relatively simple to fix: unmap the old LDT and flush TLB before
freeing the old LDT memory.
This further allows to avoid flushing the TLB in map_ldt_struct() as the
slot is unmapped and flushed by unmap_ldt_struct() or has never been mapped
at all.
[ tglx: Massaged changelog and removed the needless line breaks ]
Fixes: f55f0501cbf6 ("x86/pti: Put the LDT in its own PGD if PTI is on")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: peterz@infradead.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: bhe@redhat.com
Cc: willy@infradead.org
Cc: linux-mm@kvack.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181026122856.66224-3-kirill.shutemov@linux.intel.com
---
arch/x86/kernel/ldt.c | 51 ++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 38 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index ab18e0884dc6..18e4525c5933 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -199,14 +199,6 @@ static void sanity_check_ldt_mapping(struct mm_struct *mm)
/*
* If PTI is enabled, this maps the LDT into the kernelmode and
* usermode tables for the given mm.
- *
- * There is no corresponding unmap function. Even if the LDT is freed, we
- * leave the PTEs around until the slot is reused or the mm is destroyed.
- * This is harmless: the LDT is always in ordinary memory, and no one will
- * access the freed slot.
- *
- * If we wanted to unmap freed LDTs, we'd also need to do a flush to make
- * it useful, and the flush would slow down modify_ldt().
*/
static int
map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
@@ -214,8 +206,8 @@ map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
unsigned long va;
bool is_vmalloc;
spinlock_t *ptl;
+ int i, nr_pages;
pgd_t *pgd;
- int i;
if (!static_cpu_has(X86_FEATURE_PTI))
return 0;
@@ -238,7 +230,9 @@ map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
is_vmalloc = is_vmalloc_addr(ldt->entries);
- for (i = 0; i * PAGE_SIZE < ldt->nr_entries * LDT_ENTRY_SIZE; i++) {
+ nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE);
+
+ for (i = 0; i < nr_pages; i++) {
unsigned long offset = i << PAGE_SHIFT;
const void *src = (char *)ldt->entries + offset;
unsigned long pfn;
@@ -272,13 +266,39 @@ map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
/* Propagate LDT mapping to the user page-table */
map_ldt_struct_to_user(mm);
- va = (unsigned long)ldt_slot_va(slot);
- flush_tlb_mm_range(mm, va, va + LDT_SLOT_STRIDE, PAGE_SHIFT, false);
-
ldt->slot = slot;
return 0;
}
+static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt)
+{
+ unsigned long va;
+ int i, nr_pages;
+
+ if (!ldt)
+ return;
+
+ /* LDT map/unmap is only required for PTI */
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE);
+
+ for (i = 0; i < nr_pages; i++) {
+ unsigned long offset = i << PAGE_SHIFT;
+ spinlock_t *ptl;
+ pte_t *ptep;
+
+ va = (unsigned long)ldt_slot_va(ldt->slot) + offset;
+ ptep = get_locked_pte(mm, va, &ptl);
+ pte_clear(mm, va, ptep);
+ pte_unmap_unlock(ptep, ptl);
+ }
+
+ va = (unsigned long)ldt_slot_va(ldt->slot);
+ flush_tlb_mm_range(mm, va, va + nr_pages * PAGE_SIZE, PAGE_SHIFT, false);
+}
+
#else /* !CONFIG_PAGE_TABLE_ISOLATION */
static int
@@ -286,6 +306,10 @@ map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
{
return 0;
}
+
+static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt)
+{
+}
#endif /* CONFIG_PAGE_TABLE_ISOLATION */
static void free_ldt_pgtables(struct mm_struct *mm)
@@ -524,6 +548,7 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
}
install_ldt(mm, new_ldt);
+ unmap_ldt_struct(mm, old_ldt);
free_ldt_struct(old_ldt);
error = 0;
next prev parent reply other threads:[~2018-11-06 20:41 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-26 12:28 [PATCHv3 0/3] Fix couple of issues with LDT remap for PTI Kirill A. Shutemov
2018-10-26 12:28 ` [PATCHv3 1/3] x86/mm: Move LDT remap out of KASLR region on 5-level paging Kirill A. Shutemov
2018-11-02 21:07 ` Andy Lutomirski
2018-11-06 20:39 ` [tip:x86/urgent] " tip-bot for Kirill A. Shutemov
2018-11-10 12:29 ` [PATCHv3 1/3] " Baoquan He
2018-11-23 15:58 ` Kirill A. Shutemov
2018-12-03 3:01 ` Baoquan He
2018-12-03 9:26 ` Kirill A. Shutemov
2018-10-26 12:28 ` [PATCHv3 2/3] x86/ldt: Unmap PTEs for the slot before freeing LDT pages Kirill A. Shutemov
2018-10-31 12:17 ` Kirill A. Shutemov
2018-11-06 20:40 ` tip-bot for Kirill A. Shutemov [this message]
2018-10-26 12:28 ` [PATCHv3 3/3] x86/ldt: Remove unused variable in map_ldt_struct() Kirill A. Shutemov
2018-11-02 21:08 ` Andy Lutomirski
2018-11-06 20:40 ` [tip:x86/urgent] " tip-bot for Kirill A. Shutemov
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