[PATCH v6 10/22] powerpc/book3s64/pkeys: Store/restore userspace AMR/IAMR correctly on entry and exit from kernel
Aneesh Kumar K.V
aneesh.kumar at linux.ibm.com
Thu Nov 26 00:55:13 AEDT 2020
On 11/25/20 7:22 PM, Christophe Leroy wrote:
>
>
> Le 25/11/2020 à 06:16, Aneesh Kumar K.V a écrit :
>> This prepare kernel to operate with a different value than userspace
>> AMR/IAMR.
>> For this, AMR/IAMR need to be saved and restored on entry and return
>> from the
>> kernel.
>>
>> With KUAP we modify kernel AMR when accessing user address from the
>> kernel
>> via copy_to/from_user interfaces. We don't need to modify IAMR value in
>> similar fashion.
>>
>> If MMU_FTR_PKEY is enabled we need to save AMR/IAMR in pt_regs on
>> entering
>> kernel from userspace. If not we can assume that AMR/IAMR is not modified
>> from userspace.
>>
>> We need to save AMR if we have MMU_FTR_KUAP feature enabled and we are
>> interrupted within kernel. This is required so that if we get interrupted
>> within copy_to/from_user we continue with the right AMR value.
>>
>> If we hae MMU_FTR_KUEP enabled we need to restore IAMR on return to
>> userspace
>> beause kernel will be running with a different IAMR value.
>>
>> Reviewed-by: Sandipan Das <sandipan at linux.ibm.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
>> ---
>> arch/powerpc/include/asm/book3s/64/kup.h | 222 +++++++++++++++++++----
>> arch/powerpc/include/asm/ptrace.h | 5 +-
>> arch/powerpc/kernel/asm-offsets.c | 2 +
>> arch/powerpc/kernel/entry_64.S | 6 +-
>> arch/powerpc/kernel/exceptions-64s.S | 4 +-
>> arch/powerpc/kernel/syscall_64.c | 32 +++-
>> 6 files changed, 225 insertions(+), 46 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/book3s/64/kup.h
>> b/arch/powerpc/include/asm/book3s/64/kup.h
>> index 1d38eab83d48..4dbb2d53fd8f 100644
>> --- a/arch/powerpc/include/asm/book3s/64/kup.h
>> +++ b/arch/powerpc/include/asm/book3s/64/kup.h
>> @@ -13,17 +13,46 @@
>> #ifdef __ASSEMBLY__
>> -.macro kuap_restore_amr gpr1, gpr2
>> -#ifdef CONFIG_PPC_KUAP
>> +.macro kuap_restore_user_amr gpr1
>> +#if defined(CONFIG_PPC_PKEY)
>> BEGIN_MMU_FTR_SECTION_NESTED(67)
>> - mfspr \gpr1, SPRN_AMR
>> + /*
>> + * AMR and IAMR are going to be different when
>> + * returning to userspace.
>> + */
>> + ld \gpr1, STACK_REGS_AMR(r1)
>> + isync
>> + mtspr SPRN_AMR, \gpr1
>> + /*
>> + * Restore IAMR only when returning to userspace
>> + */
>> + ld \gpr1, STACK_REGS_IAMR(r1)
>> + mtspr SPRN_IAMR, \gpr1
>> +
>> + /* No isync required, see kuap_restore_user_amr() */
>> + END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_PKEY, 67)
>> +#endif
>> +.endm
>> +
>> +.macro kuap_restore_kernel_amr gpr1, gpr2
>> +#if defined(CONFIG_PPC_PKEY)
>> +
>> + BEGIN_MMU_FTR_SECTION_NESTED(67)
>> + /*
>> + * AMR is going to be mostly the same since we are
>> + * returning to the kernel. Compare and do a mtspr.
>> + */
>> ld \gpr2, STACK_REGS_AMR(r1)
>> + mfspr \gpr1, SPRN_AMR
>> cmpd \gpr1, \gpr2
>> - beq 998f
>> + beq 100f
>> isync
>> mtspr SPRN_AMR, \gpr2
>> - /* No isync required, see kuap_restore_amr() */
>> -998:
>> + /*
>> + * No isync required, see kuap_restore_amr()
>> + * No need to restore IAMR when returning to kernel space.
>> + */
>> +100:
>> END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 67)
>> #endif
>> .endm
>> @@ -42,23 +71,98 @@
>> .endm
>> #endif
>> +/*
>> + * if (pkey) {
>> + *
>> + * save AMR -> stack;
>> + * if (kuap) {
>> + * if (AMR != BLOCKED)
>> + * KUAP_BLOCKED -> AMR;
>> + * }
>> + * if (from_user) {
>> + * save IAMR -> stack;
>> + * if (kuep) {
>> + * KUEP_BLOCKED ->IAMR
>> + * }
>> + * }
>> + * return;
>> + * }
>> + *
>> + * if (kuap) {
>> + * if (from_kernel) {
>> + * save AMR -> stack;
>> + * if (AMR != BLOCKED)
>> + * KUAP_BLOCKED -> AMR;
>> + * }
>> + *
>> + * }
>> + */
>> .macro kuap_save_amr_and_lock gpr1, gpr2, use_cr, msr_pr_cr
>> -#ifdef CONFIG_PPC_KUAP
>> +#if defined(CONFIG_PPC_PKEY)
>> +
>> + /*
>> + * if both pkey and kuap is disabled, nothing to do
>> + */
>> + BEGIN_MMU_FTR_SECTION_NESTED(68)
>> + b 100f // skip_save_amr
>> + END_MMU_FTR_SECTION_NESTED_IFCLR(MMU_FTR_PKEY | MMU_FTR_KUAP, 68)
>> +
>> + /*
>> + * if pkey is disabled and we are entering from userspace
>> + * don't do anything.
>> + */
>> BEGIN_MMU_FTR_SECTION_NESTED(67)
>> .ifnb \msr_pr_cr
>> - bne \msr_pr_cr, 99f
>> + /*
>> + * Without pkey we are not changing AMR outside the kernel
>> + * hence skip this completely.
>> + */
>> + bne \msr_pr_cr, 100f // from userspace
>> .endif
>> + END_MMU_FTR_SECTION_NESTED_IFCLR(MMU_FTR_PKEY, 67)
>> +
>> + /*
>> + * pkey is enabled or pkey is disabled but entering from kernel
>> + */
>> mfspr \gpr1, SPRN_AMR
>> std \gpr1, STACK_REGS_AMR(r1)
>> - li \gpr2, (AMR_KUAP_BLOCKED >> AMR_KUAP_SHIFT)
>> - sldi \gpr2, \gpr2, AMR_KUAP_SHIFT
>> +
>> + /*
>> + * update kernel AMR with AMR_KUAP_BLOCKED only
>> + * if KUAP feature is enabled
>> + */
>> + BEGIN_MMU_FTR_SECTION_NESTED(69)
>> + LOAD_REG_IMMEDIATE(\gpr2, AMR_KUAP_BLOCKED)
>> cmpd \use_cr, \gpr1, \gpr2
>> - beq \use_cr, 99f
>> - // We don't isync here because we very recently entered via rfid
>> + beq \use_cr, 102f
>> + /*
>> + * We don't isync here because we very recently entered via an
>> interrupt
>> + */
>> mtspr SPRN_AMR, \gpr2
>> isync
>> -99:
>> - END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 67)
>> +102:
>> + END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 69)
>> +
>> + /*
>> + * if entering from kernel we don't need save IAMR
>> + */
>> + .ifnb \msr_pr_cr
>> + beq \msr_pr_cr, 100f // from kernel space
>> + mfspr \gpr1, SPRN_IAMR
>> + std \gpr1, STACK_REGS_IAMR(r1)
>> +
>> + /*
>> + * update kernel IAMR with AMR_KUEP_BLOCKED only
>> + * if KUEP feature is enabled
>> + */
>> + BEGIN_MMU_FTR_SECTION_NESTED(70)
>> + LOAD_REG_IMMEDIATE(\gpr2, AMR_KUEP_BLOCKED)
>> + mtspr SPRN_IAMR, \gpr2
>> + isync
>> + END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUEP, 70)
>> + .endif
>> +
>> +100: // skip_save_amr
>> #endif
>> .endm
>> @@ -66,22 +170,42 @@
>> DECLARE_STATIC_KEY_FALSE(uaccess_flush_key);
>> -#ifdef CONFIG_PPC_KUAP
>> +#ifdef CONFIG_PPC_PKEY
>> #include <asm/mmu.h>
>> #include <asm/ptrace.h>
>> -static inline void kuap_restore_amr(struct pt_regs *regs, unsigned
>> long amr)
>> +static inline void kuap_restore_user_amr(struct pt_regs *regs)
>
> While we are at changing the function's names, could we remove the _amr
> from the names in order to make it more generic and allow to re-use that
> name when we migrate PPC32 to C interrupt/syscall entries/exits ? (see
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/302a0e88e15ce4569d9619631b36248041d5ed27.1586196948.git.christophe.leroy@c-s.fr/)
>
How do you suggest we rename it? kuap_restore_user is a bit ambiguous right?
-aneesh
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