[xen master] x86/alternatives: build time check feature is in range

[patchbot@xxxxxxx]

commit a184ac74f5e0c96fdea7a6f1f66d34133e1c337a
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Sep 26 12:14:31 2024 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Sep 26 14:18:03 2024 +0100

    x86/alternatives: build time check feature is in range
    
    Ensure at build time the feature(s) used for the alternative blocks are in
    range of the featureset.
    
    No functional change intended, as all current usages are correct.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/include/asm/alternative-asm.h | 3 +++
 xen/arch/x86/include/asm/alternative.h     | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/xen/arch/x86/include/asm/alternative-asm.h 
b/xen/arch/x86/include/asm/alternative-asm.h
index 4092f5ba70..83e8594f0e 100644
--- a/xen/arch/x86/include/asm/alternative-asm.h
+++ b/xen/arch/x86/include/asm/alternative-asm.h
@@ -12,6 +12,9 @@
  * instruction. See apply_alternatives().
  */
 .macro altinstruction_entry orig, repl, feature, orig_len, repl_len, pad_len
+    .if \feature >= NCAPINTS * 32
+        .error "alternative feature outside of featureset range"
+    .endif
     .long \orig - .
     .long \repl - .
     .word \feature
diff --git a/xen/arch/x86/include/asm/alternative.h 
b/xen/arch/x86/include/asm/alternative.h
index 69555d781e..38472fb58e 100644
--- a/xen/arch/x86/include/asm/alternative.h
+++ b/xen/arch/x86/include/asm/alternative.h
@@ -7,6 +7,7 @@
 #include <xen/lib.h>
 #include <xen/stringify.h>
 #include <asm/asm-macros.h>
+#include <asm/cpufeatureset.h>
 
 struct __packed alt_instr {
     int32_t  orig_offset;   /* original instruction */
@@ -59,6 +60,9 @@ extern void alternative_branches(void);
                     alt_repl_len(n2)) "-" alt_orig_len)
 
 #define ALTINSTR_ENTRY(feature, num)                                    \
+        " .if " STR(feature) " >= " STR(NCAPINTS * 32) "\n"             \
+        " .error \"alternative feature outside of featureset range\"\n" \
+        " .endif\n"                                                     \
         " .long .LXEN%=_orig_s - .\n"             /* label           */ \
         " .long " alt_repl_s(num)" - .\n"         /* new instruction */ \
         " .word " __stringify(feature) "\n"       /* feature bit     */ \
--
generated by git-patchbot for /home/xen/git/xen.git#master