arm64: kpti: ensure patched kernel text is fetched from PoU

While the MMUs is disabled, I-cache speculation can result in
instructions being fetched from the PoC. During boot we may patch
instructions (e.g. for alternatives and jump labels), and these may be
dirty at the PoU (and stale at the PoC).

Thus, while the MMU is disabled in the KPTI pagetable fixup code we may
load stale instructions into the I-cache, potentially leading to
subsequent crashes when executing regions of code which have been
modified at runtime.

Similarly to commit:

  8ec41987436d566f ("arm64: mm: ensure patched kernel text is fetched from PoU")

... we can invalidate the I-cache after enabling the MMU to prevent such
issues.

The KPTI pagetable fixup code itself should be clean to the PoC per the
boot protocol, so no maintenance is required for this code.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 7dbf2be470f6c01d548a8d681ad4a35bd08cefaa..28a8f7b87ff069c261f2293be4b2fdc4fc31a3dd 100644 (file)
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -286,6 +286,15 @@ skip_pgd:
        msr     sctlr_el1, x18
        isb
 
+       /*
+        * Invalidate the local I-cache so that any instructions fetched
+        * speculatively from the PoC are discarded, since they may have
+        * been dynamically patched at the PoU.
+        */
+       ic      iallu
+       dsb     nsh
+       isb
+
        /* Set the flag to zero to indicate that we're all done */
        str     wzr, [flag_ptr]
        ret