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[79.53.30.11]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-485885b7bfasm6335304f8f.29.2026.09.04.05.57.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 05:57:14 -0700 (PDT) Date: Fri, 4 Sep 2026 14:55:09 +0200 From: Stefano Garzarella To: Luigi Leonardi Cc: qemu-devel@nongnu.org, Gerd Hoffmann , Ani Sinha Subject: Re: [PATCH v2 1/2] igvm: validate byte_offset before using it in parameter directives Message-ID: References: <20260904-fix_offset-v2-0-f5bb4cf6d4b0@redhat.com> <20260904-fix_offset-v2-1-f5bb4cf6d4b0@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260904-fix_offset-v2-1-f5bb4cf6d4b0@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=sgarzare@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Sep 04, 2026 at 01:42:55PM +0200, Luigi Leonardi wrote: >None of the directive handlers that place data at a byte_offset within >a parameter area validated that byte_offset actually falls within the >parameter area's size. A malformed IGVM file with byte_offset > size would >underflow the "size - byte_offset" computation used to determine >remaining space, wrapping to a huge value and defeating the size >check, then write out of bounds through param_entry->data + >byte_offset. > >Add qigvm_find_param_validate(), which looks up the parameter area, >checks byte_offset against its size, and returns the offset-adjusted >data pointer and remaining size via output parameters instead of the >raw QIgvmParameterData entry. This keeps the byte_offset arithmetic in >one place instead of repeating param_entry->data + byte_offset and >param_entry->size - byte_offset at every call site. > >Use it in the vp-count and environment-info handlers, adding an >explicit check that the fixed-size write fits in the remaining space. > >Signed-off-by: Luigi Leonardi >--- > backends/igvm.c | 68 +++++++++++++++++++++++++++++++++++------- > include/system/igvm-internal.h | 6 ++++ > 2 files changed, 63 insertions(+), 11 deletions(-) > >diff --git a/backends/igvm.c b/backends/igvm.c >index 7b7bdc72b7..8c07f2ce5e 100644 >--- a/backends/igvm.c >+++ b/backends/igvm.c >@@ -101,6 +101,39 @@ qigvm_find_param_entry(QIgvm *igvm, uint32_t parameter_area_index, > return NULL; > } > >+/* >+ * Look up a parameter area and check that param->byte_offset falls within >+ * it, in one step. On success, *data and *size are set to the >+ * offset-adjusted write location and remaining space within the parameter >+ * area, so callers never need to touch param->byte_offset themselves. >+ */ >+bool >+qigvm_find_param_validate(QIgvm *igvm, uint32_t parameter_area_index, I'm not sure about the name, but I don't have anything better to suggest, maybe qigvm_get_param_data() ? >+ const IGVM_VHS_PARAMETER *param, >+ uint8_t **data, uint32_t *size, >+ Error **errp) >+{ >+ QIgvmParameterData *param_entry; >+ >+ assert(data && size); >+ >+ param_entry = qigvm_find_param_entry(igvm, parameter_area_index, errp); >+ if (!param_entry) { >+ return false; >+ } All others qigvm_* functions returns 0 on success and != 0 on failure, should we be consistent ? Or maybe we can return the data pointer (with NULL as error). >+ >+ if (param->byte_offset > param_entry->size) { >+ error_setg(errp, >+ "IGVM: byte_offset 0x%x exceeds parameter area size 0x%x", >+ param->byte_offset, param_entry->size); >+ return false; >+ } >+ >+ *data = param_entry->data + param->byte_offset; >+ *size = param_entry->size - param->byte_offset; >+ return true; >+} >+ > static int qigvm_directive_page_data(QIgvm *ctx, const uint8_t *header_data, > Error **errp); > static int qigvm_directive_vp_context(QIgvm *ctx, const uint8_t *header_data, >@@ -682,17 +715,24 @@ static int qigvm_directive_vp_count(QIgvm *ctx, const uint8_t *header_data, > Error **errp) > { > const IGVM_VHS_PARAMETER *param = (const IGVM_VHS_PARAMETER *)header_data; >- QIgvmParameterData *param_entry; >+ uint8_t *data; >+ uint32_t size; nit: following the previous param_entry, maybe we can call them param_data and param_size all over the place. > uint32_t *vp_count; > CPUState *cpu; > >- param_entry = qigvm_find_param_entry(ctx, >- param->parameter_area_index, errp); >- if (param_entry == NULL) { >+ if (!qigvm_find_param_validate(ctx, param->parameter_area_index, param, >+ &data, &size, errp)) { >+ return -1; >+ } >+ >+ if (sizeof(*vp_count) > size) { >+ error_setg(errp, >+ "IGVM: vp-count parameter exceeds parameter area " >+ "defined in IGVM file"); > return -1; > } > >- vp_count = (uint32_t *)(param_entry->data + param->byte_offset); >+ vp_count = (uint32_t *)data; > *vp_count = 0; > CPU_FOREACH(cpu) > { >@@ -707,17 +747,23 @@ static int qigvm_directive_environment_info(QIgvm *ctx, > Error **errp) > { > const IGVM_VHS_PARAMETER *param = (const IGVM_VHS_PARAMETER *)header_data; >- QIgvmParameterData *param_entry; >+ uint8_t *data; >+ uint32_t size; > IgvmEnvironmentInfo *environmental_state; > >- param_entry = qigvm_find_param_entry(ctx, >- param->parameter_area_index, errp); >- if (param_entry == NULL) { >+ if (!qigvm_find_param_validate(ctx, param->parameter_area_index, param, >+ &data, &size, errp)) { >+ return -1; >+ } >+ >+ if (sizeof(*environmental_state) > size) { >+ error_setg(errp, >+ "IGVM: environment-info parameter exceeds parameter area " >+ "defined in IGVM file"); > return -1; > } > >- environmental_state = >- (IgvmEnvironmentInfo *)(param_entry->data + param->byte_offset); >+ environmental_state = (IgvmEnvironmentInfo *)data; > environmental_state->memory_is_shared = 1; > > return 0; >diff --git a/include/system/igvm-internal.h b/include/system/igvm-internal.h >index 9e9fa1d9af..6526b5055c 100644 >--- a/include/system/igvm-internal.h >+++ b/include/system/igvm-internal.h >@@ -81,4 +81,10 @@ QIgvmParameterData* > qigvm_find_param_entry(QIgvm *igvm, uint32_t parameter_area_index, > Error **errp); > >+bool >+qigvm_find_param_validate(QIgvm *igvm, uint32_t parameter_area_index, >+ const IGVM_VHS_PARAMETER *param, >+ uint8_t **data, uint32_t *size, >+ Error **errp); >+ > #endif > >-- >2.55.0 >