TDX attestation report ("Quote") sizes can grow with newer cryptographic schemes, so guests can no longer rely on a fixed-size buffer for the Quote. Newer TDX modules report the maximum Quote size via a TD-scope metadata field. Add a helper to query the size instead of exposing tdg_vm_rd() directly, as it can read arbitrary metadata fields. Thanks to Xu Yilun for suggesting this in an off-list discussion. Reviewed-by: Kiryl Shutsemau (Meta) Reviewed-by: Xiaoyao Li Reviewed-by: Kuppuswamy Sathyanarayanan Reviewed-by: Binbin Wu Signed-off-by: Peter Fang --- v3: - No code changes. Add Binbin's Reviewed-by. v2: - Keep the explicit (u32) cast to document the metadata field width. [Binbin] - Note that Xu Yilun's suggestion was made in an off-list discussion. [Sathya] - Drop the Assisted-by tags, as the code was not written by AI. --- arch/x86/coco/tdx/tdx.c | 19 +++++++++++++++++++ arch/x86/include/asm/shared/tdx.h | 1 + arch/x86/include/asm/tdx.h | 2 ++ 3 files changed, 22 insertions(+) diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c index 29b6f1ed59ec..fa2ed012e736 100644 --- a/arch/x86/coco/tdx/tdx.c +++ b/arch/x86/coco/tdx/tdx.c @@ -198,6 +198,25 @@ u64 tdx_hcall_get_quote(u8 *buf, size_t size) } EXPORT_SYMBOL_GPL(tdx_hcall_get_quote); +/** + * tdx_get_max_quote_size() - Get the maximum TD Quote size + * + * Read the maximum size of a TD Quote from a 4-byte TD metadata field. The TDX + * guest driver uses it to size the buffer for Quote retrieval. Older TDX + * modules do not support this field and return an error. + * + * Return: Maximum Quote size in bytes on success, or 0 on failure. + */ +u32 tdx_get_max_quote_size(void) +{ + u64 val, ret; + + ret = tdg_vm_rd(TDCS_QUOTE_MAX_SIZE, &val); + + return ret ? 0 : (u32)val; +} +EXPORT_SYMBOL_GPL(tdx_get_max_quote_size); + static void __noreturn tdx_panic(const char *msg) { struct tdx_module_args args = { diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h index f20e91d7ac35..a58751321613 100644 --- a/arch/x86/include/asm/shared/tdx.h +++ b/arch/x86/include/asm/shared/tdx.h @@ -50,6 +50,7 @@ /* TDX TD-Scope Metadata. To be used by TDG.VM.WR and TDG.VM.RD */ #define TDCS_CONFIG_FLAGS 0x1110000300000016 #define TDCS_TD_CTLS 0x1110000300000017 +#define TDCS_QUOTE_MAX_SIZE 0x9010000200000008 #define TDCS_NOTIFY_ENABLES 0x9100000000000010 #define TDCS_TOPOLOGY_ENUM_CONFIGURED 0x9100000000000019 diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h index 89e97d5761d8..a75dbbe004bd 100644 --- a/arch/x86/include/asm/tdx.h +++ b/arch/x86/include/asm/tdx.h @@ -83,6 +83,8 @@ int tdx_mcall_extend_rtmr(u8 index, u8 *data); u64 tdx_hcall_get_quote(u8 *buf, size_t size); +u32 tdx_get_max_quote_size(void); + void __init tdx_dump_attributes(u64 td_attr); void __init tdx_dump_td_ctls(u64 td_ctls); -- 2.53.0