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powerpc/security: Allow for processors that flush the link stack using the special bcctr

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If both count cache and link stack are to be flushed, and can be flushed
with the special bcctr, patch that in directly to the flush/branch nop
site.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200609070610.846703-7-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2020-06-09 17:06:09 +10:00 • committed by Michael Ellerman
parent 70d7cdaf05
commit 4d24e21cc6
2 changed files with 21 additions and 8 deletions
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2
arch/powerpc/include/asm/security_features.h
View file

@ -63,6 +63,8 @@ static inline bool security_ftr_enabled(u64 feature)
// bcctr 2,0,0 triggers a hardware assisted count cache flush
#define SEC_FTR_BCCTR_FLUSH_ASSIST 0x0000000000000800ull
// bcctr 2,0,0 triggers a hardware assisted link stack flush
#define SEC_FTR_BCCTR_LINK_FLUSH_ASSIST 0x0000000000002000ull
// Features indicating need for Spectre/Meltdown mitigations

27
arch/powerpc/kernel/security.c
View file

@ -219,24 +219,25 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, c
if (ccd)
seq_buf_printf(&s, "Indirect branch cache disabled");
if (link_stack_flush_type == BRANCH_CACHE_FLUSH_SW)
seq_buf_printf(&s, ", Software link stack flush");
} else if (count_cache_flush_type != BRANCH_CACHE_FLUSH_NONE) {
seq_buf_printf(&s, "Mitigation: Software count cache flush");
if (count_cache_flush_type == BRANCH_CACHE_FLUSH_HW)
seq_buf_printf(&s, " (hardware accelerated)");
if (link_stack_flush_type == BRANCH_CACHE_FLUSH_SW)
seq_buf_printf(&s, ", Software link stack flush");
} else if (btb_flush_enabled) {
seq_buf_printf(&s, "Mitigation: Branch predictor state flush");
} else {
seq_buf_printf(&s, "Vulnerable");
}
if (bcs || ccd || count_cache_flush_type != BRANCH_CACHE_FLUSH_NONE) {
if (link_stack_flush_type != BRANCH_CACHE_FLUSH_NONE)
seq_buf_printf(&s, ", Software link stack flush");
if (link_stack_flush_type == BRANCH_CACHE_FLUSH_HW)
seq_buf_printf(&s, " (hardware accelerated)");
}
seq_buf_printf(&s, "\n");
return s.len;
@ -435,6 +436,7 @@ static void update_branch_cache_flush(void)
patch_instruction_site(&patch__call_kvm_flush_link_stack,
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);
}
@ -445,6 +447,10 @@ static void update_branch_cache_flush(void)
link_stack_flush_type == BRANCH_CACHE_FLUSH_NONE) {
patch_instruction_site(&patch__call_flush_branch_caches,
ppc_inst(PPC_INST_NOP));
} 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));
} else {
patch_branch_site(&patch__call_flush_branch_caches,
(u64)&flush_branch_caches, BRANCH_SET_LINK);
@ -485,8 +491,13 @@ static void toggle_branch_cache_flush(bool enable)
pr_info("link-stack-flush: flush disabled.\n");
} else {
link_stack_flush_type = BRANCH_CACHE_FLUSH_SW;
pr_info("link-stack-flush: software flush enabled.\n");
if (security_ftr_enabled(SEC_FTR_BCCTR_LINK_FLUSH_ASSIST)) {
link_stack_flush_type = BRANCH_CACHE_FLUSH_HW;
pr_info("link-stack-flush: hardware flush enabled.\n");
} else {
link_stack_flush_type = BRANCH_CACHE_FLUSH_SW;
pr_info("link-stack-flush: software flush enabled.\n");
}
}
update_branch_cache_flush();