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* Add a function to check if a region overlaps with SMM. * Add a function to check if a pointer points to SMM. * Document functions in Documentation/security/smm To be used to verify data accesses in SMM. Change-Id: Ia525d2bc685377f50ecf3bdcf337a4c885488213 Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com> Signed-off-by: Christian Walter <christian.walter@9elements.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/41084 Reviewed-by: Angel Pons <th3fanbus@gmail.com> Reviewed-by: Patrick Georgi <pgeorgi@google.com> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
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x86 System Managment Mode
Introduction
The code running in System Management Mode (SMM) provides runtime services to applications running in ring0. It has a higher privilege level than ring0 and resides in the SMRAM region which cannot be accessed from ring0.
SMM can be entered by issuing System Managment Interrupts (SMIs).
Secure data exchange
In order to not leak SMM internals or accidentally overwrite parts of SMM, ring0 provided data (pointers, offsets, sizes, ...) must be checked before using them in SMM.
There exist two methods to verify data:
/* Returns true if the region overlaps with the SMM */
bool smm_region_overlaps_handler(struct region *r);
/* Returns true if the memory pointed to overlaps with SMM reserved memory. */
static inline bool smm_points_to_smram(const void *ptr, const size_t len);