[1/2] x86/alternative: Add per-vendor patching
Commit Message
From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Fri, 27 Oct 2023 13:34:12 +0200
Add the capability to apply alternatives not based on a CPU feature but
on the current vendor the machine is running on.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
arch/x86/include/asm/alternative.h | 7 ++++++-
arch/x86/kernel/alternative.c | 14 +++++++++-----
2 files changed, 15 insertions(+), 6 deletions(-)
Comments
On Fri, Oct 27, 2023 at 05:34:18PM +0200, Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@alien8.de>
> Date: Fri, 27 Oct 2023 13:34:12 +0200
>
> Add the capability to apply alternatives not based on a CPU feature but
> on the current vendor the machine is running on.
>
> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
> ---
> arch/x86/include/asm/alternative.h | 7 ++++++-
> arch/x86/kernel/alternative.c | 14 +++++++++-----
> 2 files changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
> index 65f79092c9d9..76750f8b5aba 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -8,8 +8,13 @@
>
> #define ALT_FLAGS_SHIFT 16
>
> -#define ALT_FLAG_NOT (1 << 0)
> +/* Negate the tested feature flag */
> +#define ALT_FLAG_NOT BIT(0)
> +/* Check X86_VENDOR_* instead of a feature flag */
> +#define ALT_FLAG_VENDOR BIT(1)
> +
> #define ALT_NOT(feature) ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature))
> +#define ALT_VENDOR(x86_vendor) ((ALT_FLAG_VENDOR << ALT_FLAGS_SHIFT) | (x86_vendor))
>
> #ifndef __ASSEMBLY__
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 73be3931e4f0..8b67b5c6090e 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -433,19 +433,23 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
>
> /*
> * Patch if either:
> + * - running on the respective x86 vendor
> * - feature is present
> * - feature not present but ALT_FLAG_NOT is set to mean,
> * patch if feature is *NOT* present.
> */
> - if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
> + if (a->flags & ALT_FLAG_VENDOR) {
> + if (boot_cpu_data.x86_vendor != a->cpuid) {
> + optimize_nops(instr, a->instrlen);
> + continue;
> + }
> + } else if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
> optimize_nops(instr, a->instrlen);
> continue;
> }
But what if I want to do ALT_FLAG_VENDOR | ALT_FLAG_NOT?
/me runs
On Fri, Oct 27, 2023 at 08:11:47PM +0200, Peter Zijlstra wrote:
> But what if I want to do ALT_FLAG_VENDOR | ALT_FLAG_NOT?
I knew you were gonna say that...
You sit down and you implement it. :-P
@@ -8,8 +8,13 @@
#define ALT_FLAGS_SHIFT 16
-#define ALT_FLAG_NOT (1 << 0)
+/* Negate the tested feature flag */
+#define ALT_FLAG_NOT BIT(0)
+/* Check X86_VENDOR_* instead of a feature flag */
+#define ALT_FLAG_VENDOR BIT(1)
+
#define ALT_NOT(feature) ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature))
+#define ALT_VENDOR(x86_vendor) ((ALT_FLAG_VENDOR << ALT_FLAGS_SHIFT) | (x86_vendor))
#ifndef __ASSEMBLY__
@@ -433,19 +433,23 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
/*
* Patch if either:
+ * - running on the respective x86 vendor
* - feature is present
* - feature not present but ALT_FLAG_NOT is set to mean,
* patch if feature is *NOT* present.
*/
- if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
+ if (a->flags & ALT_FLAG_VENDOR) {
+ if (boot_cpu_data.x86_vendor != a->cpuid) {
+ optimize_nops(instr, a->instrlen);
+ continue;
+ }
+ } else if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
optimize_nops(instr, a->instrlen);
continue;
}
- DPRINTK(ALT, "feat: %s%d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d)",
- (a->flags & ALT_FLAG_NOT) ? "!" : "",
- a->cpuid >> 5,
- a->cpuid & 0x1f,
+ DPRINTK(ALT, "feat: 0x%x, flags: 0x%x, old: (%pS (%px) len: %d), repl: (%px, len: %d)",
+ a->cpuid, a->flags,
instr, instr, a->instrlen,
replacement, a->replacementlen);