Merge tag 'x86_entry_for_6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 entry updates from Dave Hansen:
"A pair of x86/entry updates.
The FRED one adjusts the kernel to the latest spec. The spec change
prevents attackers from abusing kernel entry points.
The second one came about because of the LASS work[1]. It moves the
vsyscall emulation code away from depending on X86_PF_INSTR which is
not available on some CPUs. Those CPUs are pretty obscure these days,
but this still seems like the right thing to do. It also makes this
code consistent with some things that the LASS code is going to do.
- Use RIP instead of X86_PF_INSTR for vsyscall emulation
- Remove ENDBR64 from FRED entry points"
Link: https://lore.kernel.org/lkml/20250620135325.3300848-1-kirill.shutemov@linux.intel.com/ [1]
* tag 'x86_entry_for_6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/fred: Remove ENDBR64 from FRED entry points
x86/vsyscall: Do not require X86_PF_INSTR to emulate vsyscall
diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
index 29c5c32..907bd23 100644
--- a/arch/x86/entry/entry_64_fred.S
+++ b/arch/x86/entry/entry_64_fred.S
@@ -16,7 +16,7 @@
.macro FRED_ENTER
UNWIND_HINT_END_OF_STACK
- ENDBR
+ ANNOTATE_NOENDBR
PUSH_AND_CLEAR_REGS
movq %rsp, %rdi /* %rdi -> pt_regs */
.endm
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index c9103a6..6e6c0a7 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -124,7 +124,12 @@ bool emulate_vsyscall(unsigned long error_code,
if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
return false;
- if (!(error_code & X86_PF_INSTR)) {
+ /*
+ * Assume that faults at regs->ip are because of an
+ * instruction fetch. Return early and avoid
+ * emulation for faults during data accesses:
+ */
+ if (address != regs->ip) {
/* Failed vsyscall read */
if (vsyscall_mode == EMULATE)
return false;
@@ -137,12 +142,18 @@ bool emulate_vsyscall(unsigned long error_code,
}
/*
+ * X86_PF_INSTR is only set when NX is supported. When
+ * available, use it to double-check that the emulation code
+ * is only being used for instruction fetches:
+ */
+ if (cpu_feature_enabled(X86_FEATURE_NX))
+ WARN_ON_ONCE(!(error_code & X86_PF_INSTR));
+
+ /*
* No point in checking CS -- the only way to get here is a user mode
* trap to a high address, which means that we're in 64-bit user code.
*/
- WARN_ON_ONCE(address != regs->ip);
-
if (vsyscall_mode == NONE) {
warn_bad_vsyscall(KERN_INFO, regs,
"vsyscall attempted with vsyscall=none");
