Zero GPRS r14-r31 on entry into the kernel for interrupt sources to limit influence of user-space values in potential speculation gadgets. Prior to this commit, all other GPRS are reassigned during the common prologue to interrupt handlers and so need not be zeroised explicitly.
This may be done safely, without loss of register state prior to the interrupt, as the common prologue saves the initial values of non-volatiles, which are unconditionally restored in interrupt_64.S. Mitigation defaults to enabled by INTERRUPT_SANITIZE_REGISTERS. Reviewed-by: Nicholas Piggin <npig...@gmail.com> Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com> --- Resubmitting patches as their own series after v6 partially merged: Link: https://lore.kernel.org/all/166488988686.779920.13794870102696416283.b4...@ellerman.id.au/t/ --- arch/powerpc/kernel/exceptions-64e.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S index 930e36099015..6b842d5ea4e1 100644 --- a/arch/powerpc/kernel/exceptions-64e.S +++ b/arch/powerpc/kernel/exceptions-64e.S @@ -358,7 +358,6 @@ ret_from_mc_except: std r14,PACA_EXMC+EX_R14(r13); \ std r15,PACA_EXMC+EX_R15(r13) - /* Core exception code for all exceptions except TLB misses. */ #define EXCEPTION_COMMON_LVL(n, scratch, excf) \ exc_##n##_common: \ @@ -394,7 +393,8 @@ exc_##n##_common: \ std r12,STACK_FRAME_OVERHEAD-16(r1); /* mark the frame */ \ std r3,_TRAP(r1); /* set trap number */ \ std r0,RESULT(r1); /* clear regs->result */ \ - SAVE_NVGPRS(r1); + SAVE_NVGPRS(r1); \ + SANITIZE_ZEROIZE_NVGPRS(); /* minimise speculation influence */ #define EXCEPTION_COMMON(n) \ EXCEPTION_COMMON_LVL(n, SPRN_SPRG_GEN_SCRATCH, PACA_EXGEN) -- 2.37.2
