Re: [PATCH v6 30/60] i386/tdx: Wire TDX_REPORT_FATAL_ERROR with GuestPanic facility

Daniel P. Berrangé
2024-11-05T10:53:57Z

On Tue, Nov 05, 2024 at 01:23:38AM -0500, Xiaoyao Li wrote:
> Integrate TDX's TDX_REPORT_FATAL_ERROR into QEMU GuestPanic facility
>
> Originated-from: Isaku Yamahata <isaku.yamahata@intel.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
> Changes in v6:
> - change error_code of GuestPanicInformationTdx from uint64_t to
> uint32_t, to only contains the bit 31:0 returned in r12.
>
> Changes in v5:
> - mention additional error information in gpa when it presents;
> - refine the documentation; (Markus)
>
> Changes in v4:
> - refine the documentation; (Markus)
>
> Changes in v3:
> - Add docmentation of new type and struct; (Daniel)
> - refine the error message handling; (Daniel)
> ---
> qapi/run-state.json | 31 +++++++++++++++++++++--
> system/runstate.c | 58 +++++++++++++++++++++++++++++++++++++++++++
> target/i386/kvm/tdx.c | 24 +++++++++++++++++-
> 3 files changed, 110 insertions(+), 3 deletions(-)
>
> diff --git a/qapi/run-state.json b/qapi/run-state.json
> index ce95cfa46b73..c5b0b747b30d 100644
> --- a/qapi/run-state.json
> +++ b/qapi/run-state.json
> @@ -501,10 +501,12 @@
> #
> # @s390: s390 guest panic information type (Since: 2.12)
> #
> +# @tdx: tdx guest panic information type (Since: 9.0)
> +#
> # Since: 2.9
> ##
> { 'enum': 'GuestPanicInformationType',
> - 'data': [ 'hyper-v', 's390' ] }
> + 'data': [ 'hyper-v', 's390', 'tdx' ] }
>
> ##
> # @GuestPanicInformation:
> @@ -519,7 +521,8 @@
> 'base': {'type': 'GuestPanicInformationType'},
> 'discriminator': 'type',
> 'data': {'hyper-v': 'GuestPanicInformationHyperV',
> - 's390': 'GuestPanicInformationS390'}}
> + 's390': 'GuestPanicInformationS390',
> + 'tdx' : 'GuestPanicInformationTdx'}}
>
> ##
> # @GuestPanicInformationHyperV:
> @@ -598,6 +601,30 @@
> 'psw-addr': 'uint64',
> 'reason': 'S390CrashReason'}}
>
> +##
> +# @GuestPanicInformationTdx:
> +#
> +# TDX Guest panic information specific to TDX, as specified in the
> +# "Guest-Hypervisor Communication Interface (GHCI) Specification",
> +# section TDG.VP.VMCALL<ReportFatalError>.
> +#
> +# @error-code: TD-specific error code
> +#
> +# @message: Human-readable error message provided by the guest. Not
> +# to be trusted.
> +#
> +# @gpa: guest-physical address of a page that contains more verbose
> +# error information, as zero-terminated string. Present when the
> +# "GPA valid" bit (bit 63) is set in @error-code.
> +#
> +#
> +# Since: 9.0

This is very outdated. Change to 10.0 as the next possible release
it could land it.

> +##
> +{'struct': 'GuestPanicInformationTdx',
> + 'data': {'error-code': 'uint32',
> + 'message': 'str',
> + '*gpa': 'uint64'}}
> +
> ##
> # @MEMORY_FAILURE:
> #
> diff --git a/system/runstate.c b/system/runstate.c
> index c2c9afa905a6..9bb8162eb28f 100644
> --- a/system/runstate.c
> +++ b/system/runstate.c
> @@ -565,6 +565,52 @@ static void qemu_system_wakeup(void)
> }
> }
>
> +static char *tdx_parse_panic_message(char *message)
> +{
> + bool printable = false;
> + char *buf = NULL;
> + int len = 0, i;
> +
> + /*
> + * Although message is defined as a json string, we shouldn't
> + * unconditionally treat it as is because the guest generated it and
> + * it's not necessarily trustable.
> + */
> + if (message) {
> + /* The caller guarantees the NUL-terminated string. */
> + len = strlen(message);
> +
> + printable = len > 0;
> + for (i = 0; i < len; i++) {
> + if (!(0x20 <= message[i] && message[i] <= 0x7e)) {
> + printable = false;
> + break;
> + }
> + }
> + }
> +
> + if (!printable && len) {
> + /* 3 = length of "%02x " */
> + buf = g_malloc(len * 3);

....allocating memory

> + for (i = 0; i < len; i++) {
> + if (message[i] == '\0') {
> + break;
> + } else {
> + sprintf(buf + 3 * i, "%02x ", message[i]);
> + }
> + }
> + if (i > 0)
> + /* replace the last ' '(space) to NUL */
> + buf[i * 3 - 1] = '\0';
> + else
> + buf[0] = '\0';
> +
> + return buf;

....returning alllocated memory

> + }
> +
> + return message;

....returning a pointer that came from a struct field

> +}

This is a bad design - we should require the caller to always
free memory, or never free memory - not a mix.

> +
> void qemu_system_guest_panicked(GuestPanicInformation *info)
> {
> qemu_log_mask(LOG_GUEST_ERROR, "Guest crashed");
> @@ -606,7 +652,19 @@ void qemu_system_guest_panicked(GuestPanicInformation *info)
> S390CrashReason_str(info->u.s390.reason),
> info->u.s390.psw_mask,
> info->u.s390.psw_addr);
> + } else if (info->type == GUEST_PANIC_INFORMATION_TYPE_TDX) {
> + qemu_log_mask(LOG_GUEST_ERROR,
> + "\nTDX guest reports fatal error:"
> + " error code: 0x%" PRIx32 " error message:\"%s\"\n",
> + info->u.tdx.error_code,
> + tdx_parse_panic_message(info->u.tdx.message));

This is a leak in the case where tdx_parse_panic_message() returned
allocated memory.

> + if (info->u.tdx.gpa != -1ull) {
> + qemu_log_mask(LOG_GUEST_ERROR, "Additional error information "
> + "can be found at gpa page: 0x%" PRIx64 "\n",
> + info->u.tdx.gpa);
> + }
> }
> +
> qapi_free_GuestPanicInformation(info);
> }
> }

With regards,
Daniel
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