[PATCH v0 06/12] x86/mce: Prevent severity computation from being instrumented

Borislav Petkov
2021-11-04T14:41:03Z

Mark all the MCE severity computation logic noinstr and allow
instrumentation when it "calls out".

Fixes

vmlinux.o: warning: objtool: do_machine_check()+0xc5d: call to mce_severity() leaves .noinstr.text section

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/kernel/cpu/mce/severity.c | 29 ++++++++++++++++++++---------
1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
index 00e97ebbd94a..03543765e9bf 100644
--- a/arch/x86/kernel/cpu/mce/severity.c
+++ b/arch/x86/kernel/cpu/mce/severity.c
@@ -263,24 +263,35 @@ static bool is_copy_from_user(struct pt_regs *regs)
* distinguish an exception taken in user from from one
* taken in the kernel.
*/
-static int error_context(struct mce *m, struct pt_regs *regs)
+static noinstr int error_context(struct mce *m, struct pt_regs *regs)
{
+ int fixup_type;
+ bool copy_user;
+
if ((m->cs & 3) == 3)
return IN_USER;
+
if (!mc_recoverable(m->mcgstatus))
return IN_KERNEL;

- switch (ex_get_fixup_type(m->ip)) {
+ instrumentation_begin();
+ fixup_type = ex_get_fixup_type(m->ip);
+ copy_user = is_copy_from_user(regs);
+ instrumentation_end();
+
+ switch (fixup_type) {
case EX_TYPE_UACCESS:
case EX_TYPE_COPY:
- if (!regs || !is_copy_from_user(regs))
+ if (!regs || !copy_user)
return IN_KERNEL;
m->kflags |= MCE_IN_KERNEL_COPYIN;
fallthrough;
+
case EX_TYPE_FAULT_MCE_SAFE:
case EX_TYPE_DEFAULT_MCE_SAFE:
m->kflags |= MCE_IN_KERNEL_RECOV;
return IN_KERNEL_RECOV;
+
default:
return IN_KERNEL;
}
@@ -315,8 +326,8 @@ static int mce_severity_amd_smca(struct mce *m, enum context err_ctx)
* See AMD Error Scope Hierarchy table in a newer BKDG. For example
* 49125_15h_Models_30h-3Fh_BKDG.pdf, section "RAS Features"
*/
-static int mce_severity_amd(struct mce *m, struct pt_regs *regs, int tolerant,
- char **msg, bool is_excp)
+static noinstr int mce_severity_amd(struct mce *m, struct pt_regs *regs, int tolerant,
+ char **msg, bool is_excp)
{
enum context ctx = error_context(m, regs);

@@ -368,8 +379,8 @@ static int mce_severity_amd(struct mce *m, struct pt_regs *regs, int tolerant,
return MCE_KEEP_SEVERITY;
}

-static int mce_severity_intel(struct mce *m, struct pt_regs *regs,
- int tolerant, char **msg, bool is_excp)
+static noinstr int mce_severity_intel(struct mce *m, struct pt_regs *regs,
+ int tolerant, char **msg, bool is_excp)
{
enum exception excp = (is_excp ? EXCP_CONTEXT : NO_EXCP);
enum context ctx = error_context(m, regs);
@@ -405,8 +416,8 @@ static int mce_severity_intel(struct mce *m, struct pt_regs *regs,
}
}

-int mce_severity(struct mce *m, struct pt_regs *regs, int tolerant, char **msg,
- bool is_excp)
+int noinstr mce_severity(struct mce *m, struct pt_regs *regs, int tolerant, char **msg,
+ bool is_excp)
{
if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
--
2.29.2