From 97228ca375c78bfd960767dcd4919c981add306f Mon Sep 17 00:00:00 2001 From: Benjamin Gray Date: Mon, 19 Jun 2023 17:36:26 +1000 Subject: [PATCH] powerpc/ptrace: Expose HASHKEYR register to ptrace 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 Reviewed-by: Russell Currey Signed-off-by: Michael Ellerman Link: https://msgid.link/20230616034846.311705-8-bgray@linux.ibm.com --- 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 f1032fe626f4..3910cd7bb2d9 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, (u64)lower_32_bits(mfspr(SPRN_HDEXCR_RO))); } +#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 */