This patch provides the implementation of execute-only pkey. The architecture-independent layer expects the arch-dependent layer, to support the ability to create and enable a special key which has execute-only permission.
Acked-by: Balbir Singh bsingharora@gmail.com Signed-off-by: Ram Pai linuxram@us.ibm.com --- arch/powerpc/include/asm/book3s/64/mmu.h | 1 + arch/powerpc/include/asm/pkeys.h | 6 +++- arch/powerpc/mm/pkeys.c | 58 ++++++++++++++++++++++++++++++ 3 files changed, 64 insertions(+), 1 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h index 37ef23c..0abeb0e 100644 --- a/arch/powerpc/include/asm/book3s/64/mmu.h +++ b/arch/powerpc/include/asm/book3s/64/mmu.h @@ -116,6 +116,7 @@ struct patb_entry { * bit unset -> key available for allocation */ u32 pkey_allocation_map; + s16 execute_only_pkey; /* key holding execute-only protection */ #endif } mm_context_t;
diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h index 3def5af..2b5bb35 100644 --- a/arch/powerpc/include/asm/pkeys.h +++ b/arch/powerpc/include/asm/pkeys.h @@ -128,9 +128,13 @@ static inline int mm_pkey_free(struct mm_struct *mm, int pkey) * Try to dedicate one of the protection keys to be used as an * execute-only protection key. */ +extern int __execute_only_pkey(struct mm_struct *mm); static inline int execute_only_pkey(struct mm_struct *mm) { - return 0; + if (static_branch_likely(&pkey_disabled)) + return -1; + + return __execute_only_pkey(mm); }
static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma, diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c index 7dfcf2d..b466a2c 100644 --- a/arch/powerpc/mm/pkeys.c +++ b/arch/powerpc/mm/pkeys.c @@ -96,6 +96,8 @@ void pkey_mm_init(struct mm_struct *mm) if (static_branch_likely(&pkey_disabled)) return; mm_pkey_allocation_map(mm) = initial_allocation_mask; + /* -1 means unallocated or invalid */ + mm->context.execute_only_pkey = -1; }
static inline u64 read_amr(void) @@ -260,3 +262,59 @@ void thread_pkey_regs_init(struct thread_struct *thread) write_iamr(read_iamr() & pkey_iamr_mask); write_uamor(read_uamor() & pkey_amr_uamor_mask); } + +static inline bool pkey_allows_readwrite(int pkey) +{ + int pkey_shift = pkeyshift(pkey); + + if (!is_pkey_enabled(pkey)) + return true; + + return !(read_amr() & ((AMR_RD_BIT|AMR_WR_BIT) << pkey_shift)); +} + +int __execute_only_pkey(struct mm_struct *mm) +{ + bool need_to_set_mm_pkey = false; + int execute_only_pkey = mm->context.execute_only_pkey; + int ret; + + /* Do we need to assign a pkey for mm's execute-only maps? */ + if (execute_only_pkey == -1) { + /* Go allocate one to use, which might fail */ + execute_only_pkey = mm_pkey_alloc(mm); + if (execute_only_pkey < 0) + return -1; + need_to_set_mm_pkey = true; + } + + /* + * We do not want to go through the relatively costly dance to set AMR + * if we do not need to. Check it first and assume that if the + * execute-only pkey is readwrite-disabled than we do not have to set it + * ourselves. + */ + if (!need_to_set_mm_pkey && !pkey_allows_readwrite(execute_only_pkey)) + return execute_only_pkey; + + /* + * Set up AMR so that it denies access for everything other than + * execution. + */ + ret = __arch_set_user_pkey_access(current, execute_only_pkey, + PKEY_DISABLE_ACCESS | + PKEY_DISABLE_WRITE); + /* + * If the AMR-set operation failed somehow, just return 0 and + * effectively disable execute-only support. + */ + if (ret) { + mm_pkey_free(mm, execute_only_pkey); + return -1; + } + + /* We got one, store it and use it from here on out */ + if (need_to_set_mm_pkey) + mm->context.execute_only_pkey = execute_only_pkey; + return execute_only_pkey; +}