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[otbn] Patch an error in the OTBN boot services program #27679

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[otbn] Patch an error in the OTBN boot services program #27679

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17 changes: 17 additions & 0 deletions sw/device/silicon_creator/lib/drivers/otbn.c
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Original file line number Diff line number Diff line change
Expand Up @@ -264,3 +264,20 @@ rom_error_t sc_otbn_load_app(const sc_otbn_app_t app) {
}
return kErrorOk;
}

void sc_otbn_patch(void) {
enum {
// Offset in the code of the bad instruction:
kBugOffset = 0x958,
// The bad instruction is:
// bn.rshi w16, w20, w31 >> 192
kBadInstr = 0xc1fa387b,
// The good instruction is:
// bn.rshi w16, w31, w20 >> 192
kGoodInstr = 0xc14fb87b,
};
uint32_t inst = abs_mmio_read32(kBase + OTBN_IMEM_REG_OFFSET + kBugOffset);
if (inst == kBadInstr) {
abs_mmio_write32(kBase + OTBN_IMEM_REG_OFFSET + kBugOffset, kGoodInstr);
}
}
12 changes: 12 additions & 0 deletions sw/device/silicon_creator/lib/drivers/otbn.h
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Expand Up @@ -322,6 +322,18 @@ rom_error_t sc_otbn_imem_sec_wipe(void);
OT_WARN_UNUSED_RESULT
rom_error_t sc_otbn_dmem_sec_wipe(void);

/**
* Patch a bad instruction in OTBN imem.
*
* There is a bug in the OTBN boot services program loaded by ROM. There is a
* single instruction with mistakenly transposed operands which can affect the
* random share values. This bug DOES NOT affect the correctness of the OTBN
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Suggested change
* random share values. This bug DOES NOT affect the correctness of the OTBN
* random share values. This bug DOES NOT affect the correctness of the OTBN

* calculations.
*
* This function patches the bad instruction with the correctly instruction.
*/
void sc_otbn_patch(void);

#ifdef __cplusplus
}
#endif
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1 change: 1 addition & 0 deletions sw/device/silicon_creator/rom_ext/imm_section/BUILD
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Expand Up @@ -48,6 +48,7 @@ cc_library(
"//sw/device/silicon_creator/lib/base:static_dice",
"//sw/device/silicon_creator/lib/cert:dice_chain",
"//sw/device/silicon_creator/lib/drivers:flash_ctrl",
"//sw/device/silicon_creator/lib/drivers:otbn",
"//sw/device/silicon_creator/lib/drivers:rnd",
"//sw/device/silicon_creator/lib/ownership:ownership_key",
"//sw/device/silicon_creator/rom_ext:rom_ext_manifest",
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8 changes: 8 additions & 0 deletions sw/device/silicon_creator/rom_ext/imm_section/imm_section.c
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Expand Up @@ -11,6 +11,7 @@
#include "sw/device/silicon_creator/lib/base/sec_mmio.h"
#include "sw/device/silicon_creator/lib/cert/dice_chain.h"
#include "sw/device/silicon_creator/lib/drivers/flash_ctrl.h"
#include "sw/device/silicon_creator/lib/drivers/otbn.h"
#include "sw/device/silicon_creator/lib/drivers/rnd.h"
#include "sw/device/silicon_creator/lib/epmp_state.h"
#include "sw/device/silicon_creator/lib/error.h"
Expand All @@ -21,6 +22,13 @@

OT_WARN_UNUSED_RESULT
static rom_error_t imm_section_start(void) {
// Patch a bug in the OTBN ECDSA-P256 program.
//
// There is a single instruction with mistakenly transposed operands which
// can affect the random share values. This bug DOES NOT affect the
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// can affect the random share values. This bug DOES NOT affect the
// can affect the random share values. This bug DOES NOT affect the

// correctness of the OTBN calculations.
sc_otbn_patch();

// Check the ePMP state.
HARDENED_RETURN_IF_ERROR(epmp_state_check());
// Check sec_mmio expectations.
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