Re: [Qemu-devel] [PATCH qemu] target/ppc: Yet another fix for KVM-HV HPTE accessors

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Jan 11, 2018 at 03:08:32PM +1100, Alexey Kardashevskiy wrote:
> As stated in the 1ad9f0a464fe commit log, the returned entries are not
> a while PTEG. It was not a problem before 1ad9f0a464fe as it would read
> a single record assuming it contains a whole PTEG but now the code tries
> reading the entire PTEG and "if ((n - i) < invalid)" produces negative
> values which then are converted to size_t for memset() and that throws
> seg fault.
> 
> This fixes the math.
> 
> While here, fix the last @i increment as well.
> 
> Fixes: 1ad9f0a464fe "target/ppc: Fix KVM-HV HPTE accessors"
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Applied, thanks.

> ---
> 
> Record #0:
> (gdb) p *hdr
> $13 = {
>   index = <ptr>,
>   n_valid = 0x1,
>   n_invalid = 0x6
> }
> 
> Record #1:
> (gdb) p *hdr
> $18 = {
>   index = <ptr>,
>   n_valid = 0x2,
>   n_invalid = 0x6
> }
> 
> 
> i.e. in the second iteration of the loop right before
> "if ((n - i) < invalid)":
> (gdb) p n
> $16 = 0x8
> (gdb) p i
> $17 = 0x9
> 
> and @invalid becomes -1.
> 
> ---
>  target/ppc/kvm.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 0566af7..c2dea81 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2657,21 +2657,24 @@ void kvmppc_read_hptes(ppc_hash_pte64_t *hptes, hwaddr ptex, int n)
>  
>          hdr = (struct kvm_get_htab_header *)buf;
>          while ((i < n) && ((char *)hdr < (buf + rc))) {
> -            int invalid = hdr->n_invalid;
> +            int invalid = hdr->n_invalid, valid = hdr->n_valid;
>  
>              if (hdr->index != (ptex + i)) {
>                  hw_error("kvmppc_read_hptes: Unexpected HPTE index %"PRIu32
>                           " != (%"HWADDR_PRIu" + %d", hdr->index, ptex, i);
>              }
>  
> -            memcpy(hptes + i, hdr + 1, HASH_PTE_SIZE_64 * hdr->n_valid);
> -            i += hdr->n_valid;
> +            if (n - i < valid) {
> +                valid = n - i;
> +            }
> +            memcpy(hptes + i, hdr + 1, HASH_PTE_SIZE_64 * valid);
> +            i += valid;
>  
>              if ((n - i) < invalid) {
>                  invalid = n - i;
>              }
>              memset(hptes + i, 0, invalid * HASH_PTE_SIZE_64);
> -            i += hdr->n_invalid;
> +            i += invalid;
>  
>              hdr = (struct kvm_get_htab_header *)
>                  ((char *)(hdr + 1) + HASH_PTE_SIZE_64 * hdr->n_valid);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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