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Subject[PATCH v2 2/2] powerpc/kvm: don't crash on missing rng, and use darn
Date
On POWER8 systems that don't have ibm,power-rng available, a guest that
ignores the KVM_CAP_PPC_HWRNG flag and calls H_RANDOM anyway will
dereference a NULL pointer. And on machines with darn instead of
ibm,power-rng, H_RANDOM won't work at all.

This patch kills two birds with one stone, by routing H_RANDOM calls to
ppc_md.get_random_seed, and doing the real mode check inside of it.

Cc: stable@vger.kernel.org # v4.1+
Cc: Michael Ellerman <mpe@ellerman.id.au>
Fixes: e928e9cb3601 ("KVM: PPC: Book3S HV: Add fast real-mode H_RANDOM implementation.")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
arch/powerpc/include/asm/archrandom.h | 5 ----
arch/powerpc/kvm/book3s_hv_builtin.c | 7 +++---
arch/powerpc/platforms/powernv/rng.c | 33 +++++++--------------------
3 files changed, 12 insertions(+), 33 deletions(-)

diff --git a/arch/powerpc/include/asm/archrandom.h b/arch/powerpc/include/asm/archrandom.h
index 11d4815841ab..3af27bb84a3d 100644
--- a/arch/powerpc/include/asm/archrandom.h
+++ b/arch/powerpc/include/asm/archrandom.h
@@ -38,12 +38,7 @@ static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
#endif /* CONFIG_ARCH_RANDOM */

#ifdef CONFIG_PPC_POWERNV
-int pnv_hwrng_present(void);
int pnv_get_random_long(unsigned long *v);
-int pnv_get_random_real_mode(unsigned long *v);
-#else
-static inline int pnv_hwrng_present(void) { return 0; }
-static inline int pnv_get_random_real_mode(unsigned long *v) { return 0; }
#endif

#endif /* _ASM_POWERPC_ARCHRANDOM_H */
diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
index 799d40c2ab4f..3abaef5f9ac2 100644
--- a/arch/powerpc/kvm/book3s_hv_builtin.c
+++ b/arch/powerpc/kvm/book3s_hv_builtin.c
@@ -19,7 +19,7 @@
#include <asm/interrupt.h>
#include <asm/kvm_ppc.h>
#include <asm/kvm_book3s.h>
-#include <asm/archrandom.h>
+#include <asm/machdep.h>
#include <asm/xics.h>
#include <asm/xive.h>
#include <asm/dbell.h>
@@ -176,13 +176,14 @@ EXPORT_SYMBOL_GPL(kvmppc_hcall_impl_hv_realmode);

int kvmppc_hwrng_present(void)
{
- return pnv_hwrng_present();
+ return ppc_md.get_random_seed != NULL;
}
EXPORT_SYMBOL_GPL(kvmppc_hwrng_present);

long kvmppc_rm_h_random(struct kvm_vcpu *vcpu)
{
- if (pnv_get_random_real_mode(&vcpu->arch.regs.gpr[4]))
+ if (ppc_md.get_random_seed &&
+ ppc_md.get_random_seed(&vcpu->arch.regs.gpr[4]))
return H_SUCCESS;

return H_HARDWARE;
diff --git a/arch/powerpc/platforms/powernv/rng.c b/arch/powerpc/platforms/powernv/rng.c
index 868bb9777425..c748567cd47e 100644
--- a/arch/powerpc/platforms/powernv/rng.c
+++ b/arch/powerpc/platforms/powernv/rng.c
@@ -29,15 +29,6 @@ struct pnv_rng {

static DEFINE_PER_CPU(struct pnv_rng *, pnv_rng);

-int pnv_hwrng_present(void)
-{
- struct pnv_rng *rng;
-
- rng = get_cpu_var(pnv_rng);
- put_cpu_var(rng);
- return rng != NULL;
-}
-
static unsigned long rng_whiten(struct pnv_rng *rng, unsigned long val)
{
unsigned long parity;
@@ -58,17 +49,6 @@ static unsigned long rng_whiten(struct pnv_rng *rng, unsigned long val)
return val;
}

-int pnv_get_random_real_mode(unsigned long *v)
-{
- struct pnv_rng *rng;
-
- rng = raw_cpu_read(pnv_rng);
-
- *v = rng_whiten(rng, __raw_rm_readq(rng->regs_real));
-
- return 1;
-}
-
static int pnv_get_random_darn(unsigned long *v)
{
unsigned long val;
@@ -105,11 +85,14 @@ int pnv_get_random_long(unsigned long *v)
{
struct pnv_rng *rng;

- rng = get_cpu_var(pnv_rng);
-
- *v = rng_whiten(rng, in_be64(rng->regs));
-
- put_cpu_var(rng);
+ if (mfmsr() & MSR_DR) {
+ rng = raw_cpu_read(pnv_rng);
+ *v = rng_whiten(rng, __raw_rm_readq(rng->regs_real));
+ } else {
+ rng = get_cpu_var(pnv_rng);
+ *v = rng_whiten(rng, in_be64(rng->regs));
+ put_cpu_var(rng);
+ }

return 1;
}
--
2.35.1
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