[PATCH] powerpc/security: Fix link stack flush instruction
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2020-10-07 08:08:22
The inline execution path for the hardware assisted branch flush
instruction failed to set CTR to the correct value before bcctr,
causing a crash when the feature is enabled.
Fixes: 4d24e21cc694 ("powerpc/security: Allow for processors that flush the link stack using the special bcctr")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
arch/powerpc/include/asm/asm-prototypes.h | 4 ++-
arch/powerpc/kernel/entry_64.S | 8 ++++--
arch/powerpc/kernel/security.c | 34 ++++++++++++++++-------
3 files changed, 33 insertions(+), 13 deletions(-)
diff --git a/arch/powerpc/include/asm/asm-prototypes.h b/arch/powerpc/include/asm/asm-prototypes.h
index de14b1a34d56..9652756b0694 100644
--- a/arch/powerpc/include/asm/asm-prototypes.h
+++ b/arch/powerpc/include/asm/asm-prototypes.h@@ -144,7 +144,9 @@ void _kvmppc_restore_tm_pr(struct kvm_vcpu *vcpu, u64 guest_msr); void _kvmppc_save_tm_pr(struct kvm_vcpu *vcpu, u64 guest_msr); /* Patch sites */ -extern s32 patch__call_flush_branch_caches; +extern s32 patch__call_flush_branch_caches1; +extern s32 patch__call_flush_branch_caches2; +extern s32 patch__call_flush_branch_caches3; extern s32 patch__flush_count_cache_return; extern s32 patch__flush_link_stack_return; extern s32 patch__call_kvm_flush_link_stack;
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 733e40eba4eb..2f3846192ec7 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S@@ -430,7 +430,11 @@ _ASM_NOKPROBE_SYMBOL(save_nvgprs); #define FLUSH_COUNT_CACHE \ 1: nop; \ - patch_site 1b, patch__call_flush_branch_caches + patch_site 1b, patch__call_flush_branch_caches1; \ +1: nop; \ + patch_site 1b, patch__call_flush_branch_caches2; \ +1: nop; \ + patch_site 1b, patch__call_flush_branch_caches3 .macro nops number .rept \number
@@ -512,7 +516,7 @@ _GLOBAL(_switch) kuap_check_amr r9, r10 - FLUSH_COUNT_CACHE + FLUSH_COUNT_CACHE /* Clobbers r9, ctr */ /* * On SMP kernels, care must be taken because a task may be
diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index c9876aab3142..e4e1a94ccf6a 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c@@ -430,30 +430,44 @@ device_initcall(stf_barrier_debugfs_init); static void update_branch_cache_flush(void) { + u32 *site; + #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE + site = &patch__call_kvm_flush_link_stack; // This controls the branch from guest_exit_cont to kvm_flush_link_stack if (link_stack_flush_type == BRANCH_CACHE_FLUSH_NONE) { - patch_instruction_site(&patch__call_kvm_flush_link_stack, - ppc_inst(PPC_INST_NOP)); + patch_instruction_site(site, ppc_inst(PPC_INST_NOP)); } else { // Could use HW flush, but that could also flush count cache - patch_branch_site(&patch__call_kvm_flush_link_stack, - (u64)&kvm_flush_link_stack, BRANCH_SET_LINK); + patch_branch_site(site, (u64)&kvm_flush_link_stack, BRANCH_SET_LINK); } #endif + // Patch out the bcctr first, then nop the rest + site = &patch__call_flush_branch_caches3; + patch_instruction_site(site, ppc_inst(PPC_INST_NOP)); + site = &patch__call_flush_branch_caches2; + patch_instruction_site(site, ppc_inst(PPC_INST_NOP)); + site = &patch__call_flush_branch_caches1; + patch_instruction_site(site, ppc_inst(PPC_INST_NOP)); + // This controls the branch from _switch to flush_branch_caches if (count_cache_flush_type == BRANCH_CACHE_FLUSH_NONE && link_stack_flush_type == BRANCH_CACHE_FLUSH_NONE) { - patch_instruction_site(&patch__call_flush_branch_caches, - ppc_inst(PPC_INST_NOP)); + // Nothing to be done + } else if (count_cache_flush_type == BRANCH_CACHE_FLUSH_HW && link_stack_flush_type == BRANCH_CACHE_FLUSH_HW) { - patch_instruction_site(&patch__call_flush_branch_caches, - ppc_inst(PPC_INST_BCCTR_FLUSH)); + // Patch in the bcctr last + site = &patch__call_flush_branch_caches1; + patch_instruction_site(site, ppc_inst(0x39207fff)); // li r9,0x7fff + site = &patch__call_flush_branch_caches2; + patch_instruction_site(site, ppc_inst(0x7d2903a6)); // mtctr r9 + site = &patch__call_flush_branch_caches3; + patch_instruction_site(site, ppc_inst(PPC_INST_BCCTR_FLUSH)); + } else { - patch_branch_site(&patch__call_flush_branch_caches, - (u64)&flush_branch_caches, BRANCH_SET_LINK); + patch_branch_site(site, (u64)&flush_branch_caches, BRANCH_SET_LINK); // If we just need to flush the link stack, early return if (count_cache_flush_type == BRANCH_CACHE_FLUSH_NONE) {
--
2.23.0