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Subject[patch 14/16] x86/ldt: Prepare for VMA mapping
From: Thomas Gleixner <tglx@linutronix.de>

Implement that infrastructure to manage LDT information with backing
pages. Preparatory patch for VMA based LDT mapping. Split out for ease of
review.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/include/asm/mmu.h | 3 +
arch/x86/include/asm/mmu_context.h | 9 ++-
arch/x86/kernel/ldt.c | 107 ++++++++++++++++++++++++++++++++++++-
3 files changed, 116 insertions(+), 3 deletions(-)

--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -7,6 +7,8 @@
#include <linux/mutex.h>
#include <linux/atomic.h>

+struct ldt_mapping;
+
/*
* x86 has arch-specific MMU state beyond what lives in mm_struct.
*/
@@ -29,6 +31,7 @@ typedef struct {

#ifdef CONFIG_MODIFY_LDT_SYSCALL
struct rw_semaphore ldt_usr_sem;
+ struct ldt_mapping *ldt_mapping;
struct ldt_struct *ldt;
#endif

--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -42,6 +42,8 @@ static inline void load_mm_cr4(struct mm
#include <asm/ldt.h>

#define LDT_ENTRIES_MAP_SIZE (LDT_ENTRIES * LDT_ENTRY_SIZE)
+#define LDT_ENTRIES_PAGES (LDT_ENTRIES_MAP_SIZE / PAGE_SIZE)
+#define LDT_ENTRIES_PER_PAGE (PAGE_SIZE / LDT_ENTRY_SIZE)

/*
* ldt_structs can be allocated, used, and freed, but they are never
@@ -54,8 +56,10 @@ struct ldt_struct {
* call gates. On native, we could merge the ldt_struct and LDT
* allocations, but it's not worth trying to optimize.
*/
- struct desc_struct *entries;
- unsigned int nr_entries;
+ struct desc_struct *entries;
+ struct page *pages[LDT_ENTRIES_PAGES];
+ unsigned int nr_entries;
+ unsigned int pages_allocated;
};

/*
@@ -65,6 +69,7 @@ static inline void init_new_context_ldt(
struct mm_struct *mm)
{
mm->context.ldt = NULL;
+ mm->context.ldt_mapping = NULL;
init_rwsem(&mm->context.ldt_usr_sem);
/*
* Set the TIF flag unconditonally as in ldt_dup_context() the new
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -28,6 +28,11 @@
#include <asm/mmu_context.h>
#include <asm/syscalls.h>

+struct ldt_mapping {
+ struct ldt_struct ldts[2];
+ unsigned int ldt_index;
+};
+
/* After calling this, the LDT is immutable. */
static void finalize_ldt_struct(struct ldt_struct *ldt)
{
@@ -82,6 +87,97 @@ static void install_ldt(struct mm_struct
mutex_unlock(&mm->context.lock);
}

+static void ldt_free_pages(struct ldt_struct *ldt)
+{
+ int i;
+
+ for (i = 0; i < ldt->pages_allocated; i++)
+ __free_page(ldt->pages[i]);
+}
+
+static void ldt_free_lmap(struct ldt_mapping *lmap)
+{
+ if (!lmap)
+ return;
+ ldt_free_pages(&lmap->ldts[0]);
+ ldt_free_pages(&lmap->ldts[1]);
+ kfree(lmap);
+}
+
+static int ldt_alloc_pages(struct ldt_struct *ldt, unsigned int nentries)
+{
+ unsigned int npages, idx;
+
+ npages = DIV_ROUND_UP(nentries * LDT_ENTRY_SIZE, PAGE_SIZE);
+
+ for (idx = ldt->pages_allocated; idx < npages; idx++) {
+ if (WARN_ON_ONCE(ldt->pages[idx]))
+ continue;
+
+ ldt->pages[idx] = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ if (!ldt->pages[idx])
+ return -ENOMEM;
+
+ ldt->pages_allocated++;
+ }
+ return 0;
+}
+
+static struct ldt_mapping *ldt_alloc_lmap(struct mm_struct *mm,
+ unsigned int nentries)
+{
+ struct ldt_mapping *lmap = kzalloc(sizeof(*lmap), GFP_KERNEL);
+
+ if (!lmap)
+ return ERR_PTR(-ENOMEM);
+
+ if (ldt_alloc_pages(&lmap->ldts[0], nentries)) {
+ ldt_free_lmap(lmap);
+ return ERR_PTR(-ENOMEM);
+ }
+ return lmap;
+}
+
+static void ldt_set_entry(struct ldt_struct *ldt, struct desc_struct *ldtdesc,
+ unsigned int offs)
+{
+ unsigned int dstidx;
+
+ offs *= LDT_ENTRY_SIZE;
+ dstidx = offs / PAGE_SIZE;
+ offs %= PAGE_SIZE;
+ memcpy(page_address(ldt->pages[dstidx]) + offs, ldtdesc,
+ sizeof(*ldtdesc));
+}
+
+static void ldt_clone_entries(struct ldt_struct *dst, struct ldt_struct *src,
+ unsigned int nent)
+{
+ unsigned long tocopy;
+ unsigned int i;
+
+ for (i = 0, tocopy = nent * LDT_ENTRY_SIZE; tocopy; i++) {
+ unsigned long n = min(PAGE_SIZE, tocopy);
+
+ memcpy(page_address(dst->pages[i]),
+ page_address(src->pages[i]), n);
+ tocopy -= n;
+ }
+}
+
+static void cleanup_ldt_struct(struct ldt_struct *ldt)
+{
+ static struct desc_struct zero_desc;
+ unsigned int i;
+
+ if (!ldt)
+ return;
+ paravirt_free_ldt(ldt->entries, ldt->nr_entries);
+ for (i = 0; i < ldt->nr_entries; i++)
+ ldt_set_entry(ldt, &zero_desc, i);
+ ldt->nr_entries = 0;
+}
+
/*
* ldt_write_fault() already checked whether there is an ldt installed in
* __do_page_fault(), so it's safe to access it here because interrupts are
@@ -202,8 +298,17 @@ int ldt_dup_context(struct mm_struct *ol
*/
void destroy_context_ldt(struct mm_struct *mm)
{
- free_ldt_struct(mm->context.ldt);
+ struct ldt_mapping *lmap = mm->context.ldt_mapping;
+ struct ldt_struct *ldt = mm->context.ldt;
+
+ free_ldt_struct(ldt);
mm->context.ldt = NULL;
+
+ if (!lmap)
+ return;
+
+ mm->context.ldt_mapping = NULL;
+ ldt_free_lmap(lmap);
}

/*

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