Re: [PATCH 1/4] acpi: fix QEMU crash when started with SLIC table

[Igor Mammedov]

CCing, qemu-stable@

On Mon, 27 Dec 2021 14:31:17 -0500
Igor Mammedov <imammedo@redhat.com> wrote:

> if QEMU is started with used provided SLIC table blob,
> 
>   -acpitable sig=SLIC,oem_id='CRASH 
> ',oem_table_id="ME",oem_rev=00002210,asl_compiler_id="",asl_compiler_rev=00000000,data=/dev/null
> it will assert with:
> 
>   hw/acpi/aml-build.c:61:build_append_padded_str: assertion failed: (len <= 
> maxlen)
> 
> and following backtrace:
> 
>   ...
>   build_append_padded_str (array=0x555556afe320, str=0x555556afdb2e "CRASH 
> ME", maxlen=0x6, pad=0x20) at hw/acpi/aml-build.c:61
>   acpi_table_begin (desc=0x7fffffffd1b0, array=0x555556afe320) at 
> hw/acpi/aml-build.c:1727
>   build_fadt (tbl=0x555556afe320, linker=0x555557ca3830, f=0x7fffffffd318, 
> oem_id=0x555556afdb2e "CRASH ME", oem_table_id=0x555556afdb34 "ME") at 
> hw/acpi/aml-build.c:2064
>   ...
> 
> which happens due to acpi_table_begin() expecting NULL terminated
> oem_id and oem_table_id strings, which is normally the case, but
> in case of user provided SLIC table, oem_id points to table's blob
> directly and as result oem_id became longer than expected.
> 
> Fix issue by handling oem_id consistently and make acpi_get_slic_oem()
> return NULL terminated strings.
> 
> PS:
> After [1] refactoring, oem_id semantics became inconsistent, where
> NULL terminated string was coming from machine and old way pointer
> into byte array coming from -acpitable option. That used to work
> since build_header() wasn't expecting NULL terminated string and
> blindly copied the 1st 6 bytes only.
> 
> However commit [2] broke that by replacing build_header() with
> acpi_table_begin(), which was expecting NULL terminated string
> and was checking oem_id size.
> 
> 1) 602b45820 ("acpi: Permit OEM ID and OEM table ID fields to be changed")
> 2)
> Fixes: 4b56e1e4eb08 ("acpi: build_fadt: use 
> acpi_table_begin()/acpi_table_end() instead of build_header()")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/786
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  hw/acpi/core.c       | 4 ++--
>  hw/i386/acpi-build.c | 2 ++
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/acpi/core.c b/hw/acpi/core.c
> index 1e004d0078..3e811bf03c 100644
> --- a/hw/acpi/core.c
> +++ b/hw/acpi/core.c
> @@ -345,8 +345,8 @@ int acpi_get_slic_oem(AcpiSlicOem *oem)
>          struct acpi_table_header *hdr = (void *)(u - sizeof(hdr->_length));
>  
>          if (memcmp(hdr->sig, "SLIC", 4) == 0) {
> -            oem->id = hdr->oem_id;
> -            oem->table_id = hdr->oem_table_id;
> +            oem->id = g_strndup(hdr->oem_id, 6);
> +            oem->table_id = g_strndup(hdr->oem_table_id, 8);
>              return 0;
>          }
>      }
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 8383b83ee3..0234fe7588 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -2723,6 +2723,8 @@ void acpi_build(AcpiBuildTables *tables, MachineState 
> *machine)
>  
>      /* Cleanup memory that's no longer used. */
>      g_array_free(table_offsets, true);
> +    g_free(slic_oem.id);
> +    g_free(slic_oem.table_id);
>  }
>  
>  static void acpi_ram_update(MemoryRegion *mr, GArray *data)