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powerpc/64e: Clear gprs on interrupt routine entry on Book3E 

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 <npiggin@gmail.com>
Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221201071019.1953023-6-rmclure@linux.ibm.com
This commit is contained in:
Rohan McLure 2022-12-01 18:10:18 +11:00 committed by Michael Ellerman
parent 1df45d78b8
commit efe1691ac8
1 changed files with 2 additions and 2 deletions
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4
arch/powerpc/kernel/exceptions-64e.S
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@ -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_INT_FRAME_MARKER(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_NVGPRS(); /* minimise speculation influence */
#define EXCEPTION_COMMON(n) \
EXCEPTION_COMMON_LVL(n, SPRN_SPRG_GEN_SCRATCH, PACA_EXGEN)