[PATCH v3 25/41] powerpc/book3s64/kuep: Store/restore userspace IAMR correctly on entry and exit from kernel
Aneesh Kumar K.V
aneesh.kumar at linux.ibm.com
Wed Jun 10 19:51:48 AEST 2020
This prepare kernel to operate with a different value than userspace IAMR.
For this, IAMR needs to be saved and restored on entry and return from the
kernel.
If MMU_FTR_KEY is enabled we always use the key mechanism to implement KUEP
feature. If MMU_FTR_KEY is not supported and if we support MMU_FTR_KUEP
(radix translation on POWER9), we can skip restoring IAMR on return
to userspace. Userspace won't be using IAMR in that specific config.
We don't need to save/restore IAMR on reentry into the kernel due to interrupt
because the kernel doesn't modify IAMR internally.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
---
arch/powerpc/include/asm/book3s/64/kup.h | 46 ++++++++++++++++++++++--
arch/powerpc/include/asm/ptrace.h | 6 +++-
arch/powerpc/kernel/asm-offsets.c | 4 +++
arch/powerpc/kernel/syscall_64.c | 8 +++--
4 files changed, 59 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
index 82bef3901672..f26f3fad5872 100644
--- a/arch/powerpc/include/asm/book3s/64/kup.h
+++ b/arch/powerpc/include/asm/book3s/64/kup.h
@@ -17,15 +17,26 @@
#if defined(CONFIG_PPC_MEM_KEYS)
BEGIN_MMU_FTR_SECTION_NESTED(67)
/*
- * AMR is going to be different when
+ * AMR and IAMR are going to be different when
* returning to userspace.
*/
ld \gpr1, STACK_REGS_KUAP(r1)
isync
mtspr SPRN_AMR, \gpr1
+ /*
+ * Restore IAMR only when returning to userspace
+ */
+ ld \gpr1, STACK_REGS_KUEP(r1)
+ mtspr SPRN_IAMR, \gpr1
/* No isync required, see kuap_restore_user_amr() */
END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_PKEY , 67)
+
+ /*
+ * We don't check KUEP feature here, because if FTR_PKEY
+ * is not enabled we don't need to restore IAMR on
+ * return to usespace.
+ */
#endif
.endm
@@ -53,6 +64,9 @@
isync
mtspr SPRN_AMR, \gpr2
/* No isync required, see kuap_restore_amr() */
+ /*
+ * No need to restore IAMR when returning to kernel space.
+ */
100: // skip_restore_amr
#endif
.endm
@@ -90,6 +104,12 @@
b 100f // skip_save_amr
ALT_MMU_FTR_SECTION_END_NESTED_IFSET(MMU_FTR_KUAP, 68)
+ /*
+ * We don't check KUEP feature here, because if FTR_PKEY
+ * is not enabled we don't need to save IAMR on
+ * entry from usespace. That is handled by either
+ * handle_kuap_save_amr or skip_save_amr
+ */
99: // handle_kuap_save_amr
.ifnb \msr_pr_cr
@@ -120,6 +140,25 @@
102:
END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 69)
+ .ifnb \msr_pr_cr
+ beq \msr_pr_cr, 103f // from kernel space
+ mfspr \gpr1, SPRN_IAMR
+ std \gpr1, STACK_REGS_KUEP(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)
+ cmpd \use_cr, \gpr1, \gpr2
+ beq \use_cr, 103f
+ mtspr SPRN_IAMR, \gpr2
+ isync
+103:
+ END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUEP, 70)
+ .endif
+
100: // skip_save_amr
#endif
.endm
@@ -140,13 +179,13 @@ static inline void kuap_restore_user_amr(struct pt_regs *regs)
isync();
mtspr(SPRN_AMR, regs->kuap);
+ mtspr(SPRN_IAMR, regs->kuep);
/*
* No isync required here because we are about to rfi
* back to previous context before any user accesses
* would be made, which is a CSI.
*/
}
-
static inline void kuap_restore_kernel_amr(struct pt_regs *regs,
unsigned long amr)
{
@@ -162,6 +201,9 @@ static inline void kuap_restore_kernel_amr(struct pt_regs *regs,
*/
}
}
+ /*
+ * No need to restore IAMR when returning to kernel space.
+ */
}
static inline unsigned long kuap_get_and_check_amr(void)
diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index ac3970fff0d5..8e6601c984fd 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -56,8 +56,12 @@ struct pt_regs
#ifdef CONFIG_PPC_KUAP
unsigned long kuap;
#endif
+#ifdef CONFIG_PPC_KUEP
+ unsigned long kuep;
+#endif
+
};
- unsigned long __pad[2]; /* Maintain 16 byte interrupt stack alignment */
+ unsigned long __pad[4]; /* Maintain 16 byte interrupt stack alignment */
};
};
#endif
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 9b9cde07e396..37a52a3d500b 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -357,6 +357,10 @@ int main(void)
#ifdef CONFIG_PPC_KUAP
STACK_PT_REGS_OFFSET(STACK_REGS_KUAP, kuap);
#endif
+#ifdef CONFIG_PPC_KUEP
+ STACK_PT_REGS_OFFSET(STACK_REGS_KUEP, kuep);
+#endif
+
#if defined(CONFIG_PPC32)
#if defined(CONFIG_BOOKE) || defined(CONFIG_40x)
diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall_64.c
index fded67982fbe..8229730c6cb5 100644
--- a/arch/powerpc/kernel/syscall_64.c
+++ b/arch/powerpc/kernel/syscall_64.c
@@ -37,15 +37,19 @@ notrace long system_call_exception(long r3, long r4, long r5,
#ifdef CONFIG_PPC_MEM_KEYS
if (mmu_has_feature(MMU_FTR_PKEY)) {
- unsigned long amr;
+ unsigned long amr, iamr;
/*
- * When entering from userspace we mostly have the AMR
+ * When entering from userspace we mostly have the AMR/IAMR
* different from kernel default values. Hence don't compare.
*/
amr = mfspr(SPRN_AMR);
+ iamr = mfspr(SPRN_IAMR);
regs->kuap = amr;
+ regs->kuep = iamr;
if (mmu_has_feature(MMU_FTR_KUAP))
mtspr(SPRN_AMR, AMR_KUAP_BLOCKED);
+ if (mmu_has_feature(MMU_FTR_KUEP))
+ mtspr(SPRN_IAMR, AMR_KUEP_BLOCKED);
isync();
} else
#endif
--
2.26.2
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