[PATCH 5.18 27/70] x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value

Greg Kroah-Hartman
2022-07-22T09:10:49Z

From: Peter Zijlstra <peterz@infradead.org>

commit caa0ff24d5d0e02abce5e65c3d2b7f20a6617be5 upstream.

Due to TIF_SSBD and TIF_SPEC_IB the actual IA32_SPEC_CTRL value can
differ from x86_spec_ctrl_base. As such, keep a per-CPU value
reflecting the current task's MSR content.

[jpoimboe: rename]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/nospec-branch.h | 1 +
arch/x86/kernel/cpu/bugs.c | 28 +++++++++++++++++++++++-----
arch/x86/kernel/process.c | 2 +-
3 files changed, 25 insertions(+), 6 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -253,6 +253,7 @@ static inline void indirect_branch_predi

/* The Intel SPEC CTRL MSR base value cache */
extern u64 x86_spec_ctrl_base;
+extern void write_spec_ctrl_current(u64 val);

/*
* With retpoline, we must use IBRS to restrict branch prediction
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -49,12 +49,30 @@ static void __init mmio_select_mitigatio
static void __init srbds_select_mitigation(void);
static void __init l1d_flush_select_mitigation(void);

-/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
+/* The base value of the SPEC_CTRL MSR without task-specific bits set */
u64 x86_spec_ctrl_base;
EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
+
+/* The current value of the SPEC_CTRL MSR with task-specific bits set */
+DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
+EXPORT_SYMBOL_GPL(x86_spec_ctrl_current);
+
static DEFINE_MUTEX(spec_ctrl_mutex);

/*
+ * Keep track of the SPEC_CTRL MSR value for the current task, which may differ
+ * from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update().
+ */
+void write_spec_ctrl_current(u64 val)
+{
+ if (this_cpu_read(x86_spec_ctrl_current) == val)
+ return;
+
+ this_cpu_write(x86_spec_ctrl_current, val);
+ wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
+
+/*
* The vendor and possibly platform specific bits which can be modified in
* x86_spec_ctrl_base.
*/
@@ -1272,7 +1290,7 @@ static void __init spectre_v2_select_mit
if (spectre_v2_in_eibrs_mode(mode)) {
/* Force it so VMEXIT will restore correctly */
x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);
}

switch (mode) {
@@ -1327,7 +1345,7 @@ static void __init spectre_v2_select_mit

static void update_stibp_msr(void * __unused)
{
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);
}

/* Update x86_spec_ctrl_base in case SMT state changed. */
@@ -1570,7 +1588,7 @@ static enum ssb_mitigation __init __ssb_
x86_amd_ssb_disable();
} else {
x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);
}
}

@@ -1821,7 +1839,7 @@ int arch_prctl_spec_ctrl_get(struct task
void x86_spec_ctrl_setup_ap(void)
{
if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);

if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
x86_amd_ssb_disable();
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -600,7 +600,7 @@ static __always_inline void __speculatio
}

if (updmsr)
- wrmsrl(MSR_IA32_SPEC_CTRL, msr);
+ write_spec_ctrl_current(msr);
}

static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)