[PATCH] x86/ldt: Rename ldr_struct.size to .n_entries

From: Borislav Petkov
Date: Tue Jun 06 2017 - 13:31:43 EST

From: Borislav Petkov <bp@xxxxxxx>

... because this is exactly what it is: the number of entries in the
LDT. Calling it "size" is simply confusing and it is actually begging
to be called "n_entries" or somesuch, especially if you see constructs
like:

alloc_size = size * LDT_ENTRY_SIZE;

since LDT_ENTRY_SIZE is the size of a single entry.

There should be no functionality change resulting from this patch, as
the before/after output from tools/testing/selftests/x86/ldt_gdt.c
shows.

Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
arch/x86/events/core.c | 2 +-
arch/x86/include/asm/mmu_context.h | 4 ++--
arch/x86/kernel/ldt.c | 49 +++++++++++++++++++-------------------
arch/x86/kernel/process_64.c | 2 +-
arch/x86/kernel/step.c | 2 +-
arch/x86/math-emu/fpu_system.h | 2 +-
6 files changed, 31 insertions(+), 30 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 400bea15f97e..c12b72f6972a 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2342,7 +2342,7 @@ static unsigned long get_segment_base(unsigned int segment)

/* IRQs are off, so this synchronizes with smp_store_release */
ldt = lockless_dereference(current->active_mm->context.ldt);
- if (!ldt || idx > ldt->size)
+ if (!ldt || idx > ldt->n_entries)
return 0;

desc = &ldt->entries[idx];
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index f20d7ea47095..435b43f77ab3 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -47,7 +47,7 @@ struct ldt_struct {
* allocations, but it's not worth trying to optimize.
*/
struct desc_struct *entries;
- unsigned int size;
+ unsigned int n_entries;
};

/*
@@ -87,7 +87,7 @@ static inline void load_mm_ldt(struct mm_struct *mm)
*/

if (unlikely(ldt))
- set_ldt(ldt->entries, ldt->size);
+ set_ldt(ldt->entries, ldt->n_entries);
else
clear_LDT();
#else
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index de503e7a64ad..79aa4e56ee3b 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -31,16 +31,16 @@ static void flush_ldt(void *__mm)
return;

pc = &mm->context;
- set_ldt(pc->ldt->entries, pc->ldt->size);
+ set_ldt(pc->ldt->entries, pc->ldt->n_entries);
}

/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
-static struct ldt_struct *alloc_ldt_struct(unsigned int size)
+static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
{
struct ldt_struct *new_ldt;
unsigned int alloc_size;

- if (size > LDT_ENTRIES)
+ if (num_entries > LDT_ENTRIES)
return NULL;

new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
@@ -48,7 +48,7 @@ static struct ldt_struct *alloc_ldt_struct(unsigned int size)
return NULL;

BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
- alloc_size = size * LDT_ENTRY_SIZE;
+ alloc_size = num_entries * LDT_ENTRY_SIZE;

/*
* Xen is very picky: it requires a page-aligned LDT that has no
@@ -66,14 +66,14 @@ static struct ldt_struct *alloc_ldt_struct(unsigned int size)
return NULL;
}

- new_ldt->size = size;
+ new_ldt->n_entries = num_entries;
return new_ldt;
}

/* After calling this, the LDT is immutable. */
static void finalize_ldt_struct(struct ldt_struct *ldt)
{
- paravirt_alloc_ldt(ldt->entries, ldt->size);
+ paravirt_alloc_ldt(ldt->entries, ldt->n_entries);
}

/* context.lock is held */
@@ -92,8 +92,8 @@ static void free_ldt_struct(struct ldt_struct *ldt)
if (likely(!ldt))
return;

- paravirt_free_ldt(ldt->entries, ldt->size);
- if (ldt->size * LDT_ENTRY_SIZE > PAGE_SIZE)
+ paravirt_free_ldt(ldt->entries, ldt->n_entries);
+ if (ldt->n_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
vfree_atomic(ldt->entries);
else
free_page((unsigned long)ldt->entries);
@@ -123,14 +123,14 @@ int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm)
goto out_unlock;
}

- new_ldt = alloc_ldt_struct(old_mm->context.ldt->size);
+ new_ldt = alloc_ldt_struct(old_mm->context.ldt->n_entries);
if (!new_ldt) {
retval = -ENOMEM;
goto out_unlock;
}

memcpy(new_ldt->entries, old_mm->context.ldt->entries,
- new_ldt->size * LDT_ENTRY_SIZE);
+ new_ldt->n_entries * LDT_ENTRY_SIZE);
finalize_ldt_struct(new_ldt);

mm->context.ldt = new_ldt;
@@ -153,9 +153,9 @@ void destroy_context_ldt(struct mm_struct *mm)

static int read_ldt(void __user *ptr, unsigned long bytecount)
{
- int retval;
- unsigned long size;
struct mm_struct *mm = current->mm;
+ unsigned long entries_size;
+ int retval;

mutex_lock(&mm->context.lock);

@@ -167,18 +167,18 @@ static int read_ldt(void __user *ptr, unsigned long bytecount)
if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;

- size = mm->context.ldt->size * LDT_ENTRY_SIZE;
- if (size > bytecount)
- size = bytecount;
+ entries_size = mm->context.ldt->n_entries * LDT_ENTRY_SIZE;
+ if (entries_size > bytecount)
+ entries_size = bytecount;

- if (copy_to_user(ptr, mm->context.ldt->entries, size)) {
+ if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
retval = -EFAULT;
goto out_unlock;
}

- if (size != bytecount) {
+ if (entries_size != bytecount) {
/* Zero-fill the rest and pretend we read bytecount bytes. */
- if (clear_user(ptr + size, bytecount - size)) {
+ if (clear_user(ptr + entries_size, bytecount - entries_size)) {
retval = -EFAULT;
goto out_unlock;
}
@@ -209,7 +209,7 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
{
struct mm_struct *mm = current->mm;
struct ldt_struct *new_ldt, *old_ldt;
- unsigned int oldsize, newsize;
+ unsigned int old_n_entries, new_n_entries;
struct user_desc ldt_info;
struct desc_struct ldt;
int error;
@@ -248,17 +248,18 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)

mutex_lock(&mm->context.lock);

- old_ldt = mm->context.ldt;
- oldsize = old_ldt ? old_ldt->size : 0;
- newsize = max(ldt_info.entry_number + 1, oldsize);
+ old_ldt = mm->context.ldt;
+ old_n_entries = old_ldt ? old_ldt->n_entries : 0;
+ new_n_entries = max(ldt_info.entry_number + 1, old_n_entries);

error = -ENOMEM;
- new_ldt = alloc_ldt_struct(newsize);
+ new_ldt = alloc_ldt_struct(new_n_entries);
if (!new_ldt)
goto out_unlock;

if (old_ldt)
- memcpy(new_ldt->entries, old_ldt->entries, oldsize * LDT_ENTRY_SIZE);
+ memcpy(new_ldt->entries, old_ldt->entries, old_n_entries * LDT_ENTRY_SIZE);
+
new_ldt->entries[ldt_info.entry_number] = ldt;
finalize_ldt_struct(new_ldt);

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index b6840bf3940b..95c76edc4587 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -142,7 +142,7 @@ void release_thread(struct task_struct *dead_task)
pr_warn("WARNING: dead process %s still has LDT? <%p/%d>\n",
dead_task->comm,
dead_task->mm->context.ldt->entries,
- dead_task->mm->context.ldt->size);
+ dead_task->mm->context.ldt->n_entries);
BUG();
}
#endif
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index f07f83b3611b..59b8b9470ed6 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -34,7 +34,7 @@ unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *re

mutex_lock(&child->mm->context.lock);
if (unlikely(!child->mm->context.ldt ||
- seg >= child->mm->context.ldt->size))
+ seg >= child->mm->context.ldt->n_entries))
addr = -1L; /* bogus selector, access would fault */
else {
desc = &child->mm->context.ldt->entries[seg];
diff --git a/arch/x86/math-emu/fpu_system.h b/arch/x86/math-emu/fpu_system.h
index 5e044d506b7a..8252636e8136 100644
--- a/arch/x86/math-emu/fpu_system.h
+++ b/arch/x86/math-emu/fpu_system.h
@@ -27,7 +27,7 @@ static inline struct desc_struct FPU_get_ldt_descriptor(unsigned seg)
#ifdef CONFIG_MODIFY_LDT_SYSCALL
seg >>= 3;
mutex_lock(&current->mm->context.lock);
- if (current->mm->context.ldt && seg < current->mm->context.ldt->size)
+ if (current->mm->context.ldt && seg < current->mm->context.ldt->n_entries)
ret = current->mm->context.ldt->entries[seg];
mutex_unlock(&current->mm->context.lock);
#endif
--
2.13.0