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.ku...@linux.ibm.com>
---
arch/powerpc/include/asm/book3s/64/kup.h | 51 +++++++++++++++++++++++-
arch/powerpc/include/asm/ptrace.h | 6 ++-
arch/powerpc/kernel/asm-offsets.c | 4 ++
arch/powerpc/kernel/syscall_64.c | 5 ++-
4 files changed, 62 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/kup.h
b/arch/powerpc/include/asm/book3s/64/kup.h
index 85645d1b7102..717c2c4d3681 100644
--- a/arch/powerpc/include/asm/book3s/64/kup.h
+++ b/arch/powerpc/include/asm/book3s/64/kup.h
@@ -25,6 +25,13 @@
b 100f // skip_restore_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 restore IAMR on
+ * return to usespace. That is handled by either
+ * handle_kuap_restore_amr or skip_restore_amr
+ */
+
99: // handle_kuap_restore_amr
/*
* No key support, don't bother to restore AMR
@@ -37,7 +44,17 @@
ld \gpr, STACK_REGS_KUAP(r1)
isync
mtspr SPRN_AMR, \gpr
- /* No isync here because we will return to a different context */
+
+ /*
+ * Restore IAMR only when returning to userspace
+ */
+ .ifnb \to_user
+ ld \gpr, STACK_REGS_KUEP(r1)
+ mtspr SPRN_IAMR, \gpr
+ .endif
+ /*
+ * No isync here because we will return to a different context
+ */
100: // skip_restore_amr
#endif
.endm
@@ -75,6 +92,12 @@
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
@@ -103,7 +126,26 @@
mtspr SPRN_AMR, \gpr2
isync
102:
- END_MMU_FTR_SECTION_NESTED_IFSET(MMU_FTR_KUAP, 69)
+ 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 KUAP 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
@@ -129,6 +171,11 @@ static inline void kuap_restore_amr(struct pt_regs *regs,
bool to_user)
* returning to a different context using rfid
*/
}
+ /*
+ * We do support FTR_PKEY, restore IAMR when returning to user
+ */
+ if (to_user)
+ mtspr(SPRN_IAMR, regs->kuep);
}
static inline void kuap_check_amr(void)
diff --git a/arch/powerpc/include/asm/ptrace.h
b/arch/powerpc/include/asm/ptrace.h
index e0195e6b892b..2bfd2b6a72ab 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 fcf24a365fc0..6c7326fc73b9 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -353,6 +353,10 @@ 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 f69b4774f3b3..458f2bb80c6d 100644
--- a/arch/powerpc/kernel/syscall_64.c
+++ b/arch/powerpc/kernel/syscall_64.c
@@ -36,11 +36,14 @@ notrace long system_call_exception(long r3, long r4, long
r5,
BUG_ON(regs->softe != IRQS_ENABLED);
if (mmu_has_feature(MMU_FTR_PKEY)) {
- unsigned long amr;
+ unsigned long amr, iamr;
amr = mfspr(SPRN_AMR);
+ iamr = mfspr(SPRN_IAMR);
regs->kuap = amr;
+ regs->kuep = iamr;
mtspr(SPRN_AMR, AMR_KUAP_BLOCKED);
+ mtspr(SPRN_IAMR, AMR_KUEP_BLOCKED);
isync();
} else
kuap_check_amr();
--
2.25.3
