[PATCH 09/23] x86, kaiser: map dynamically-allocated LDTs

Dave Hansen
2017-11-23T00:39:38Z

From: Dave Hansen <dave.hansen@linux.intel.com>

Normally, a process has a NULL mm->context.ldt. But, there is a
syscall for a process to set a new one. If a process does that,
the LDT be mapped into the user page tables, just like the
default copy.

The original KAISER patch missed this case.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
Cc: Richard Fellner <richard.fellner@student.tugraz.at>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: x86@kernel.org
---

b/arch/x86/kernel/ldt.c | 25 ++++++++++++++++++++-----
1 file changed, 20 insertions(+), 5 deletions(-)

diff -puN arch/x86/kernel/ldt.c~kaiser-user-map-new-ldts arch/x86/kernel/ldt.c
--- a/arch/x86/kernel/ldt.c~kaiser-user-map-new-ldts 2017-11-22 15:45:49.059619739 -0800
+++ b/arch/x86/kernel/ldt.c 2017-11-22 15:45:49.062619739 -0800
@@ -11,6 +11,7 @@
#include <linux/gfp.h>
#include <linux/sched.h>
#include <linux/string.h>
+#include <linux/kaiser.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/syscalls.h>
@@ -57,11 +58,21 @@ static void flush_ldt(void *__mm)
refresh_ldt_segments();
}

+static void __free_ldt_struct(struct ldt_struct *ldt)
+{
+ if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
+ vfree_atomic(ldt->entries);
+ else
+ free_page((unsigned long)ldt->entries);
+ kfree(ldt);
+}
+
/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
{
struct ldt_struct *new_ldt;
unsigned int alloc_size;
+ int ret;

if (num_entries > LDT_ENTRIES)
return NULL;
@@ -89,6 +100,12 @@ static struct ldt_struct *alloc_ldt_stru
return NULL;
}

+ ret = kaiser_add_mapping((unsigned long)new_ldt->entries, alloc_size,
+ __PAGE_KERNEL | _PAGE_GLOBAL);
+ if (ret) {
+ __free_ldt_struct(new_ldt);
+ return NULL;
+ }
new_ldt->nr_entries = num_entries;
return new_ldt;
}
@@ -115,12 +132,10 @@ static void free_ldt_struct(struct ldt_s
if (likely(!ldt))
return;

+ kaiser_remove_mapping((unsigned long)ldt->entries,
+ ldt->nr_entries * LDT_ENTRY_SIZE);
paravirt_free_ldt(ldt->entries, ldt->nr_entries);
- if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
- vfree_atomic(ldt->entries);
- else
- free_page((unsigned long)ldt->entries);
- kfree(ldt);
+ __free_ldt_struct(ldt);
}

/*
_