Re: [PATCH v2 1/5] x86/mce/inject: Check if a bank is unpopulated before error injection

[Borislav Petkov]

On Tue, Oct 19, 2021 at 06:36:37PM -0500, Smita Koralahalli wrote:
> The MCA_IPID register uniquely identifies a bank's type on Scalable MCA
> (SMCA) systems. When an MCA bank is not populated, the MCA_IPID register
> will read as zero and writes to it will be ignored.
> 
> On a "hw" error injection check the value of this register before trying
> to inject the error.
> 
> Do not impose any limitation on a "sw" injection and allow the user to
> test out all the decoding paths without relying on the available hardware,
> as its purpose is to just test the code.
> 
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>
> ---
> v2:
> 	simulate -> inject.
> 	Corrected according to kernel commenting style.
> 	boot_cpu_has() -> cpu_feature_enabled().
> 	Error simulation not possible: Bank %llu unpopulated ->
> 	Cannot set IPID - bank %llu unpopulated.
> 	Used user provided IPID value on sw injection without checking
> 	underlying hardware and defined it under inj_ipid_set().
> ---
>  arch/x86/kernel/cpu/mce/inject.c | 39 +++++++++++++++++++++++++++++---
>  1 file changed, 36 insertions(+), 3 deletions(-)

So I gave it a critical look and did some modifications, see below.
Looking at those IPID MSRs - they're all read-only, which means for !sw
injection, all the module can do is check whether they're 0 - and fail
injection in that case - and do the injection otherwise.

Ok?

---
From: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>
Date: Tue, 19 Oct 2021 18:36:37 -0500
Subject: [PATCH] x86/mce/inject: Check if a bank is populated before error
 injection

The MCA_IPID register uniquely identifies a bank's type on Scalable MCA
(SMCA) systems. When an MCA bank is not populated, the MCA_IPID register
will read as zero and writes to it will be ignored.

On a hw-type error injection (injection which writes the actual MCA
registers in an attempt to cause a real MCE) check the value of this
register before trying to inject the error.

Do not impose any limitation on a sw-type injection (software-only
injection) and allow the user to test out all the decoding paths without
relying on the available hardware, as its purpose is to just test the
code.

 [ bp: Heavily massage. ]

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20211019233641.140275-2-Smita.KoralahalliChannabasappa@xxxxxxx
---
 arch/x86/kernel/cpu/mce/inject.c | 42 +++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
index 0bfc14041bbb..3333ae7886bd 100644
--- a/arch/x86/kernel/cpu/mce/inject.c
+++ b/arch/x86/kernel/cpu/mce/inject.c
@@ -74,7 +74,6 @@ MCE_INJECT_SET(status);
 MCE_INJECT_SET(misc);
 MCE_INJECT_SET(addr);
 MCE_INJECT_SET(synd);
-MCE_INJECT_SET(ipid);
 
 #define MCE_INJECT_GET(reg)						\
 static int inj_##reg##_get(void *data, u64 *val)			\
@@ -95,6 +94,20 @@ DEFINE_SIMPLE_ATTRIBUTE(status_fops, inj_status_get, inj_status_set, "%llx\n");
 DEFINE_SIMPLE_ATTRIBUTE(misc_fops, inj_misc_get, inj_misc_set, "%llx\n");
 DEFINE_SIMPLE_ATTRIBUTE(addr_fops, inj_addr_get, inj_addr_set, "%llx\n");
 DEFINE_SIMPLE_ATTRIBUTE(synd_fops, inj_synd_get, inj_synd_set, "%llx\n");
+
+/* Use the user provided IPID value on a sw injection. */
+static int inj_ipid_set(void *data, u64 val)
+{
+	struct mce *m = (struct mce *)data;
+
+	if (cpu_feature_enabled(X86_FEATURE_SMCA)) {
+		if (inj_type == SW_INJ)
+			m->ipid = val;
+	}
+
+	return 0;
+}
+
 DEFINE_SIMPLE_ATTRIBUTE(ipid_fops, inj_ipid_get, inj_ipid_set, "%llx\n");
 
 static void setup_inj_struct(struct mce *m)
@@ -577,6 +590,33 @@ static int inj_bank_set(void *data, u64 val)
 	}
 
 	m->bank = val;
+
+	/*
+	 * sw-only injection allows to write arbitrary values into the MCA registers
+	 * because it tests only the decoding paths.
+	 */
+	if (inj_type == SW_INJ)
+		goto inject;
+
+	/*
+	 * Read IPID value to determine if a bank is populated on the target
+	 * CPU.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SMCA)) {
+		u64 ipid;
+
+		if (rdmsrl_on_cpu(m->extcpu, MSR_AMD64_SMCA_MCx_IPID(val), &ipid)) {
+			pr_err("Error reading IPID on CPU%d\n", m->extcpu);
+			return -EINVAL;
+		}
+
+		if (!ipid) {
+			pr_err("Cannot inject into bank %llu - it is unpopulated\n", val);
+			return -ENODEV;
+		}
+	}
+
+inject:
 	do_inject();
 
 	/* Reset injection struct */
-- 
2.29.2

-- 
Regards/Gruss,
    Boris.

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