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x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value

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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>
This commit is contained in:
Peter Zijlstra 2022-06-14 23:15:52 +02:00 committed by Borislav Petkov
parent e8ec1b6e08
commit caa0ff24d5
3 changed files with 25 additions and 6 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
arch/x86/include/asm/nospec-branch.h
View file

@ -253,6 +253,7 @@ static inline void indirect_branch_prediction_barrier(void)
/* 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

28
arch/x86/kernel/cpu/bugs.c
View file

@ -49,11 +49,29 @@ static void __init mmio_select_mitigation(void);
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.
@ -1279,7 +1297,7 @@ static void __init spectre_v2_select_mitigation(void)
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) {
@ -1334,7 +1352,7 @@ static void __init spectre_v2_select_mitigation(void)
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. */
@ -1577,7 +1595,7 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
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);
}
}
@ -1828,7 +1846,7 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
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();

2
arch/x86/kernel/process.c
View file

@ -600,7 +600,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
}
if (updmsr)
wrmsrl(MSR_IA32_SPEC_CTRL, msr);
write_spec_ctrl_current(msr);
}
static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)