powerpc: Support prefixed instructions in alignment handler

If a prefixed instruction results in an alignment exception, the
SRR1_PREFIXED bit is set. The handler attempts to emulate the
responsible instruction and then increment the NIP past it. Use
SRR1_PREFIXED to determine by how much the NIP should be incremented.

Prefixed instructions are not permitted to cross 64-byte boundaries. If
they do the alignment interrupt is invoked with SRR1 BOUNDARY bit set.
If this occurs send a SIGBUS to the offending process if in user mode.
If in kernel mode call bad_page_fault().

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Alistair Popple <alistair@popple.id.au>
Link: https://lore.kernel.org/r/20200506034050.24806-29-jniethe5@gmail.com

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index e37bf79..051d702 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -588,6 +588,8 @@ static inline int check_io_access(struct pt_regs *regs)
 #define REASON_ILLEGAL         (ESR_PIL | ESR_PUO)
 #define REASON_PRIVILEGED      ESR_PPR
 #define REASON_TRAP            ESR_PTR
+#define REASON_PREFIXED                0
+#define REASON_BOUNDARY                0
 
 /* single-step stuff */
 #define single_stepping(regs)  (current->thread.debug.dbcr0 & DBCR0_IC)
@@ -602,12 +604,16 @@ static inline int check_io_access(struct pt_regs *regs)
 #define REASON_ILLEGAL         SRR1_PROGILL
 #define REASON_PRIVILEGED      SRR1_PROGPRIV
 #define REASON_TRAP            SRR1_PROGTRAP
+#define REASON_PREFIXED                SRR1_PREFIXED
+#define REASON_BOUNDARY                SRR1_BOUNDARY
 
 #define single_stepping(regs)  ((regs)->msr & MSR_SE)
 #define clear_single_step(regs)        ((regs)->msr &= ~MSR_SE)
 #define clear_br_trace(regs)   ((regs)->msr &= ~MSR_BE)
 #endif
 
+#define inst_length(reason)    (((reason) & REASON_PREFIXED) ? 8 : 4)
+
 #if defined(CONFIG_E500)
 int machine_check_e500mc(struct pt_regs *regs)
 {
@@ -1610,11 +1616,20 @@ void alignment_exception(struct pt_regs *regs)
 {
        enum ctx_state prev_state = exception_enter();
        int sig, code, fixed = 0;
+       unsigned long  reason;
 
        /* We restore the interrupt state now */
        if (!arch_irq_disabled_regs(regs))
                local_irq_enable();
 
+       reason = get_reason(regs);
+
+       if (reason & REASON_BOUNDARY) {
+               sig = SIGBUS;
+               code = BUS_ADRALN;
+               goto bad;
+       }
+
        if (tm_abort_check(regs, TM_CAUSE_ALIGNMENT | TM_CAUSE_PERSISTENT))
                goto bail;
 
@@ -1623,7 +1638,8 @@ void alignment_exception(struct pt_regs *regs)
                fixed = fix_alignment(regs);
 
        if (fixed == 1) {
-               regs->nip += 4; /* skip over emulated instruction */
+               /* skip over emulated instruction */
+               regs->nip += inst_length(reason);
                emulate_single_step(regs);
                goto bail;
        }
@@ -1636,6 +1652,7 @@ void alignment_exception(struct pt_regs *regs)
                sig = SIGBUS;
                code = BUS_ADRALN;
        }
+bad:
        if (user_mode(regs))
                _exception(sig, regs, code, regs->dar);
        else