This is a note to let you know that I've just added the patch titled

KVM: PPC: Book3S HV: Avoid shifts by negative amounts

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: kvm-ppc-book3s-hv-avoid-shifts-by-negative-amounts.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Fri Mar 16 15:10:48 CET 2018

From: Paul Mackerras paulus@ozlabs.org Date: Fri, 10 Nov 2017 16:40:24 +1100 Subject: KVM: PPC: Book3S HV: Avoid shifts by negative amounts

From: Paul Mackerras paulus@ozlabs.org

[ Upstream commit cda2eaa35948893d70145490d5d6ded546fc3bc6 ]

The kvmppc_hpte_page_shifts function decodes the actual and base page sizes for a HPTE, returning -1 if it doesn't recognize the page size encoding. This then gets used as a shift amount in various places, which is undefined behaviour. This was reported by Coverity.

In fact this should never occur, since we should only get HPTEs in the HPT which have a recognized page size encoding. The only place where this might not be true is in the call to kvmppc_actual_pgsz() near the beginning of kvmppc_do_h_enter(), where we are validating the HPTE value passed in from the guest.

So to fix this and eliminate the undefined behaviour, we make kvmppc_hpte_page_shifts return 0 for unrecognized page size encodings, and make kvmppc_actual_pgsz() detect that case and return 0 for the page size, which will then cause kvmppc_do_h_enter() to return an error and refuse to insert any HPTE with an unrecognized page size encoding.

To ensure that we don't get undefined behaviour in compute_tlbie_rb(), we take the 4k page size path for any unrecognized page size encoding. This should never be hit in practice because it is only used on HPTE values which have previously been checked for having a recognized page size encoding.

Signed-off-by: Paul Mackerras paulus@ozlabs.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/include/asm/kvm_book3s_64.h | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h index 735cfa35298a..998f7b7aaa9e 100644 --- a/arch/powerpc/include/asm/kvm_book3s_64.h +++ b/arch/powerpc/include/asm/kvm_book3s_64.h @@ -122,13 +122,13 @@ static inline int kvmppc_hpte_page_shifts(unsigned long h, unsigned long l) lphi = (l >> 16) & 0xf; switch ((l >> 12) & 0xf) { case 0: - return !lphi ? 24 : -1; /* 16MB */ + return !lphi ? 24 : 0; /* 16MB */ break; case 1: return 16; /* 64kB */ break; case 3: - return !lphi ? 34 : -1; /* 16GB */ + return !lphi ? 34 : 0; /* 16GB */ break; case 7: return (16 << 8) + 12; /* 64kB in 4kB */ @@ -140,7 +140,7 @@ static inline int kvmppc_hpte_page_shifts(unsigned long h, unsigned long l) return (24 << 8) + 12; /* 16MB in 4kB */ break; } - return -1; + return 0; }

static inline int kvmppc_hpte_base_page_shift(unsigned long h, unsigned long l) @@ -159,7 +159,11 @@ static inline int kvmppc_hpte_actual_page_shift(unsigned long h, unsigned long l

static inline unsigned long kvmppc_actual_pgsz(unsigned long v, unsigned long r) { - return 1ul << kvmppc_hpte_actual_page_shift(v, r); + int shift = kvmppc_hpte_actual_page_shift(v, r); + + if (shift) + return 1ul << shift; + return 0; }

static inline int kvmppc_pgsize_lp_encoding(int base_shift, int actual_shift) @@ -232,7 +236,7 @@ static inline unsigned long compute_tlbie_rb(unsigned long v, unsigned long r, va_low ^= v >> (SID_SHIFT_1T - 16); va_low &= 0x7ff;

- if (b_pgshift == 12) { + if (b_pgshift <= 12) { if (a_pgshift > 12) { sllp = (a_pgshift == 16) ? 5 : 4; rb |= sllp << 5; /* AP field */