Merge tag 'x86_cpu_for_6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 CPU feature updates from Dave Hansen:
 "The biggest thing of note here is Linear Address Space Separation
  (LASS). It represents the first time I can think of that the
  upper=>kernel/lower=>user address space convention is actually
  recognized by the hardware on x86. It ensures that userspace can not
  even get the hardware to _start_ page walks for the kernel address
  space. This, of course, is a really nice generic side channel defense.

  This is really only a down payment on LASS support. There are still
  some details to work out in its interaction with EFI calls and
  vsyscall emulation. For now, LASS is disabled if either of those
  features is compiled in (which is almost always the case).

  There's also one straggler commit in here which converts an
  under-utilized AMD CPU feature leaf into a generic Linux-defined leaf
  so more feature can be packed in there.

  Summary:

   - Enable Linear Address Space Separation (LASS)

   - Change X86_FEATURE leaf 17 from an AMD leaf to Linux-defined"

* tag 'x86_cpu_for_6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/cpu: Enable LASS during CPU initialization
  selftests/x86: Update the negative vsyscall tests to expect a #GP
  x86/traps: Communicate a LASS violation in #GP message
  x86/kexec: Disable LASS during relocate kernel
  x86/alternatives: Disable LASS when patching kernel code
  x86/asm: Introduce inline memcpy and memset
  x86/cpu: Add an LASS dependency on SMAP
  x86/cpufeatures: Enumerate the LASS feature bits
  x86/cpufeatures: Make X86_FEATURE leaf 17 Linux-specific

1 files changed, 16 insertions, 2 deletions

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index e377b06e70e3..74f4c659f9c9 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -2453,16 +2453,30 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
 __ro_after_init struct mm_struct *text_poke_mm;
 __ro_after_init unsigned long text_poke_mm_addr;
 
+/*
+ * Text poking creates and uses a mapping in the lower half of the
+ * address space. Relax LASS enforcement when accessing the poking
+ * address.
+ *
+ * objtool enforces a strict policy of "no function calls within AC=1
+ * regions". Adhere to the policy by using inline versions of
+ * memcpy()/memset() that will never result in a function call.
+ */
+
 static void text_poke_memcpy(void *dst, const void *src, size_t len)
 {
-	memcpy(dst, src, len);
+	lass_stac();
+	__inline_memcpy(dst, src, len);
+	lass_clac();
 }
 
 static void text_poke_memset(void *dst, const void *src, size_t len)
 {
 	int c = *(const int *)src;
 
-	memset(dst, c, len);
+	lass_stac();
+	__inline_memset(dst, c, len);
+	lass_clac();
 }
 
 typedef void text_poke_f(void *dst, const void *src, size_t len);