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x86/bugs: Restructure MDS mitigation

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Restructure MDS mitigation selection to use select/update/apply
functions to create consistent vulnerability handling.

  [ bp: rename and beef up comment over VERW mitigation selected var for
    maximum clarity. ]

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/20250418161721.1855190-2-david.kaplan@amd.com
This commit is contained in:
David Kaplan
2025-04-18 11:17:06 -05:00
committed by Borislav Petkov (AMD)
parent d9b79111fd
commit 559c758bc7
1 changed files with 59 additions and 2 deletions
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61
arch/x86/kernel/cpu/bugs.c
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@@ -34,6 +34,25 @@
#include "cpu.h"
/*
* Speculation Vulnerability Handling
*
* Each vulnerability is handled with the following functions:
* <vuln>_select_mitigation() -- Selects a mitigation to use. This should
* take into account all relevant command line
* options.
* <vuln>_update_mitigation() -- This is called after all vulnerabilities have
* selected a mitigation, in case the selection
* may want to change based on other choices
* made. This function is optional.
* <vuln>_apply_mitigation() -- Enable the selected mitigation.
*
* The compile-time mitigation in all cases should be AUTO. An explicit
* command-line option can override AUTO. If no such option is
* provided, <vuln>_select_mitigation() will override AUTO to the best
* mitigation option.
*/
static void __init spectre_v1_select_mitigation(void);
static void __init spectre_v2_select_mitigation(void);
static void __init retbleed_select_mitigation(void);
@@ -41,6 +60,8 @@ static void __init spectre_v2_user_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
static void __init mds_select_mitigation(void);
static void __init mds_update_mitigation(void);
static void __init mds_apply_mitigation(void);
static void __init md_clear_update_mitigation(void);
static void __init md_clear_select_mitigation(void);
static void __init taa_select_mitigation(void);
@@ -172,6 +193,7 @@ void __init cpu_select_mitigations(void)
spectre_v2_user_select_mitigation();
ssb_select_mitigation();
l1tf_select_mitigation();
mds_select_mitigation();
md_clear_select_mitigation();
srbds_select_mitigation();
l1d_flush_select_mitigation();
@@ -182,6 +204,14 @@ void __init cpu_select_mitigations(void)
*/
srso_select_mitigation();
gds_select_mitigation();
/*
* After mitigations are selected, some may need to update their
* choices.
*/
mds_update_mitigation();
mds_apply_mitigation();
}
/*
@@ -284,6 +314,12 @@ enum rfds_mitigations {
static enum rfds_mitigations rfds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_AUTO : RFDS_MITIGATION_OFF;
/*
* Set if any of MDS/TAA/MMIO/RFDS are going to enable VERW clearing
* through X86_FEATURE_CLEAR_CPU_BUF on kernel and guest entry.
*/
static bool verw_clear_cpu_buf_mitigation_selected __ro_after_init;
static void __init mds_select_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) {
@@ -294,12 +330,34 @@ static void __init mds_select_mitigation(void)
if (mds_mitigation == MDS_MITIGATION_AUTO)
mds_mitigation = MDS_MITIGATION_FULL;
if (mds_mitigation == MDS_MITIGATION_OFF)
return;
verw_clear_cpu_buf_mitigation_selected = true;
}
static void __init mds_update_mitigation(void)
{
if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())
return;
/* If TAA, MMIO, or RFDS are being mitigated, MDS gets mitigated too. */
if (verw_clear_cpu_buf_mitigation_selected)
mds_mitigation = MDS_MITIGATION_FULL;
if (mds_mitigation == MDS_MITIGATION_FULL) {
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
mds_mitigation = MDS_MITIGATION_VMWERV;
}
pr_info("%s\n", mds_strings[mds_mitigation]);
}
static void __init mds_apply_mitigation(void)
{
if (mds_mitigation == MDS_MITIGATION_FULL ||
mds_mitigation == MDS_MITIGATION_VMWERV) {
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
(mds_nosmt || cpu_mitigations_auto_nosmt()))
cpu_smt_disable(false);
@@ -602,7 +660,6 @@ static void __init md_clear_update_mitigation(void)
static void __init md_clear_select_mitigation(void)
{
mds_select_mitigation();
taa_select_mitigation();
mmio_select_mitigation();
rfds_select_mitigation();