The HASHKEYR register contains a secret per-process key to enable unique
hashes per process. In general it should not be exposed to userspace
at all and a regular process has no need to know its key.
However, checkpoint restore in userspace (CRIU) functionality requires
that a process be able to set the HASHKEYR of another process, otherwise
existing hashes on the stack would be invalidated by a new random key.
Exposing HASHKEYR in this way also makes it appear in core dumps, which
is a security concern. Multiple threads may share a key, for example
just after a fork() call, where the kernel cannot know if the child is
going to return back along the parent's stack. If such a thread is
coerced into making a core dump, then the HASHKEYR value will be
readable and able to be used against all other threads sharing that key,
effectively undoing any protection offered by hashst/hashchk.
Therefore we expose HASHKEYR to ptrace when CONFIG_CHECKPOINT_RESTORE is
enabled, providing a choice of increased security or migratable ROP
protected processes. This is similar to how ARM exposes its PAC keys.
Signed-off-by: Benjamin Gray <bg...@linux.ibm.com>
Reviewed-by: Russell Currey <rus...@russell.cc>
---
v3: * Add ruscur reviewed-by
v2: * New in v2
---
arch/powerpc/include/uapi/asm/elf.h | 1 +
arch/powerpc/kernel/ptrace/ptrace-decl.h | 3 ++
arch/powerpc/kernel/ptrace/ptrace-view.c | 36 ++++++++++++++++++++++++
include/uapi/linux/elf.h | 1 +
4 files changed, 41 insertions(+)
diff --git a/arch/powerpc/include/uapi/asm/elf.h
b/arch/powerpc/include/uapi/asm/elf.h
index e0d323c808dd..a5377f494fa3 100644
--- a/arch/powerpc/include/uapi/asm/elf.h
+++ b/arch/powerpc/include/uapi/asm/elf.h
@@ -99,6 +99,7 @@
#define ELF_NPMU 5 /* includes siar, sdar, sier, mmcr2, mmcr0 */
#define ELF_NPKEY 3 /* includes amr, iamr, uamor */
#define ELF_NDEXCR 2 /* includes dexcr, hdexcr */
+#define ELF_NHASHKEYR 1 /* includes hashkeyr */
typedef unsigned long elf_greg_t64;
typedef elf_greg_t64 elf_gregset_t64[ELF_NGREG];
diff --git a/arch/powerpc/kernel/ptrace/ptrace-decl.h
b/arch/powerpc/kernel/ptrace/ptrace-decl.h
index 998a84f64804..4171a5727197 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-decl.h
+++ b/arch/powerpc/kernel/ptrace/ptrace-decl.h
@@ -58,6 +58,9 @@ enum powerpc_regset {
REGSET_EBB, /* EBB registers */
REGSET_PMR, /* Performance Monitor Registers */
REGSET_DEXCR, /* DEXCR registers */
+#ifdef CONFIG_CHECKPOINT_RESTORE
+ REGSET_HASHKEYR, /* HASHKEYR register */
+#endif
#endif
#ifdef CONFIG_PPC_MEM_KEYS
REGSET_PKEY, /* AMR register */
diff --git a/arch/powerpc/kernel/ptrace/ptrace-view.c
b/arch/powerpc/kernel/ptrace/ptrace-view.c
index 87a46edb3efb..600fa72c2934 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-view.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-view.c
@@ -483,6 +483,35 @@ static int dexcr_get(struct task_struct *target, const
struct user_regset *regse
return membuf_store(&to, (unsigned long)(mfspr(SPRN_HDEXCR_RO) &
0xFFFFFFFF));
}
+#ifdef CONFIG_CHECKPOINT_RESTORE
+static int hashkeyr_active(struct task_struct *target, const struct
user_regset *regset)
+{
+ if (!cpu_has_feature(CPU_FTR_ARCH_31))
+ return -ENODEV;
+
+ return regset->n;
+}
+
+static int hashkeyr_get(struct task_struct *target, const struct user_regset
*regset,
+ struct membuf to)
+{
+ if (!cpu_has_feature(CPU_FTR_ARCH_31))
+ return -ENODEV;
+
+ return membuf_store(&to, target->thread.hashkeyr);
+}
+
+static int hashkeyr_set(struct task_struct *target, const struct user_regset
*regset,
+ unsigned int pos, unsigned int count, const void *kbuf,
+ const void __user *ubuf)
+{
+ if (!cpu_has_feature(CPU_FTR_ARCH_31))
+ return -ENODEV;
+
+ return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
&target->thread.hashkeyr,
+ 0, sizeof(unsigned long));
+}
+#endif /* CONFIG_CHECKPOINT_RESTORE */
#endif /* CONFIG_PPC_BOOK3S_64 */
#ifdef CONFIG_PPC_MEM_KEYS
@@ -649,6 +678,13 @@ static const struct user_regset native_regsets[] = {
.size = sizeof(u64), .align = sizeof(u64),
.active = dexcr_active, .regset_get = dexcr_get
},
+#ifdef CONFIG_CHECKPOINT_RESTORE
+ [REGSET_HASHKEYR] = {
+ .core_note_type = NT_PPC_HASHKEYR, .n = ELF_NHASHKEYR,
+ .size = sizeof(u64), .align = sizeof(u64),
+ .active = hashkeyr_active, .regset_get = hashkeyr_get, .set =
hashkeyr_set
+ },
+#endif
#endif
#ifdef CONFIG_PPC_MEM_KEYS
[REGSET_PKEY] = {
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index cfa31f1eb5d7..b705b301d88f 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -404,6 +404,7 @@ typedef struct elf64_shdr {
#define NT_PPC_TM_CDSCR 0x10f /* TM checkpointed Data Stream
Control Register */
#define NT_PPC_PKEY 0x110 /* Memory Protection Keys registers */
#define NT_PPC_DEXCR 0x111 /* PowerPC DEXCR registers */
+#define NT_PPC_HASHKEYR 0x112 /* PowerPC HASHKEYR register */
#define NT_386_TLS 0x200 /* i386 TLS slots (struct user_desc) */
#define NT_386_IOPERM 0x201 /* x86 io permission bitmap (1=deny) */
#define NT_X86_XSTATE 0x202 /* x86 extended state using xsave */
--
2.40.1
