Commit aa280a08 authored by Andrew Cooper's avatar Andrew Cooper Committed by Peter Zijlstra
Browse files

x86/fred: Correct speculative safety in fred_extint() 



array_index_nospec() is no use if the result gets spilled to the stack, as
it makes the believed safe-under-speculation value subject to memory
predictions.

For all practical purposes, this means array_index_nospec() must be used in
the expression that accesses the array.

As the code currently stands, it's the wrong side of irqentry_enter(), and
'index' is put into %ebp across the function call.

Remove the index variable and reposition array_index_nospec(), so it's
calculated immediately before the array access.

Fixes: 14619d91 ("x86/fred: FRED entry/exit and dispatch code")
Signed-off-by: default avatarAndrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260106131504.679932-1-andrew.cooper3@citrix.com
parent 6de23f81

arch/x86/entry/entry_fred.c

+2 −3
Original line number Diff line number Diff line
@@ -160,8 +160,6 @@ void __init fred_complete_exception_setup(void) 
static noinstr void fred_extint(struct pt_regs *regs)

{

	unsigned int vector = regs->fred_ss.vector;

	unsigned int index = array_index_nospec(vector - FIRST_SYSTEM_VECTOR,

						NR_SYSTEM_VECTORS);



	if (WARN_ON_ONCE(vector < FIRST_EXTERNAL_VECTOR))

		return;
@@ -170,7 +168,8 @@ static noinstr void fred_extint(struct pt_regs *regs) 
		irqentry_state_t state = irqentry_enter(regs);



		instrumentation_begin();

		sysvec_table[index](regs);

		sysvec_table[array_index_nospec(vector - FIRST_SYSTEM_VECTOR,

						NR_SYSTEM_VECTORS)](regs);

		instrumentation_end();

		irqentry_exit(regs, state);

	} else {