token_unseal: wield three unsealing authorities
diff --git a/sdk/core/loader/boot.cc b/sdk/core/loader/boot.cc
index 9aabbb0..bc67535 100644
--- a/sdk/core/loader/boot.cc
+++ b/sdk/core/loader/boot.cc
@@ -1267,15 +1267,31 @@
sizeof(void *),
PermissionSet{Permission::Global, Permission::Unseal});
- setSealingKey(imgHdr.allocator(), Allocator);
+ /*
+ * The token library unseals both static and dynamic objects, sometimes
+ * either and sometimes with static knowledge of which is expected. To
+ * avoid `li; csetaddr; csetbounds` sequences, we give it a separate cap
+ * for each case.
+ */
setSealingKey(imgHdr.token_library(),
Allocator,
2, // Allocator and StaticToken
0,
PermissionSet{Permission::Global, Permission::Unseal});
+ setSealingKey(imgHdr.token_library(),
+ StaticToken,
+ 1,
+ sizeof(void *),
+ PermissionSet{Permission::Global, Permission::Unseal});
+ setSealingKey(imgHdr.token_library(),
+ Allocator,
+ 1,
+ 2 * sizeof(void *),
+ PermissionSet{Permission::Global, Permission::Unseal});
+
constexpr size_t DynamicSealingLength =
std::numeric_limits<ptraddr_t>::max() - FirstDynamicSoftware + 1;
-
+ setSealingKey(imgHdr.allocator(), Allocator);
setSealingKey(imgHdr.allocator(),
FirstDynamicSoftware,
DynamicSealingLength,
diff --git a/sdk/core/token_library/token_unseal.S b/sdk/core/token_library/token_unseal.S
index 1dccc04..8528d72 100644
--- a/sdk/core/token_library/token_unseal.S
+++ b/sdk/core/token_library/token_unseal.S
@@ -2,15 +2,34 @@
#include <cheri-builtins.h>
#include "../allocator/token.h"
- .hidden __sealingkey
- .type __sealingkey,@object
- .section .sealing_key1,"aw",@progbits
- .globl __sealingkey
- .p2align 3
-__sealingkey:
- .chericap 0
- .size __sealingkey, 8
+.include "assembly-helpers.s"
+ .hidden __sealingkey_either
+ .type __sealingkey_either,@object
+ .section .sealing_key1,"aw",@progbits
+ .globl __sealingkey_either
+ .p2align 3
+__sealingkey_either:
+ .chericap 0
+ .size __sealingkey_either, 8
+
+ .hidden __sealingkey_static
+ .type __sealingkey_static,@object
+ .section .sealing_key2,"aw",@progbits
+ .globl __sealingkey_static
+ .p2align 3
+__sealingkey_static:
+ .chericap 0
+ .size __sealingkey_static, 8
+
+ .hidden __sealingkey_dynamic
+ .type __sealingkey_dynamic,@object
+ .section .sealing_key3,"aw",@progbits
+ .globl __sealingkey_dynamic
+ .p2align 3
+__sealingkey_dynamic:
+ .chericap 0
+ .size __sealingkey_dynamic, 8
.section .text,"ax",@progbits
@@ -19,21 +38,20 @@
/**
* The core of unsealing:
*
- * void *token_unseal_internal(struct SKeyStruct *, struct SObjStruct *, int);
+ * void *token_unseal_internal(
+ * struct SKeyStruct *, struct SObjStruct *, void *);
*/
-
.Ltoken_unseal_internal:
/*
* Register allocation:
*
- * - ca0 holds a sealing key, either the user's or the real deal, and is
- * replaced with the unsealed value or NULL
+ * - ca0 holds the user's sealing key, and is replaced with the unsealed
+ * value or NULL
*
* - ca1 holds the user's sealed object pointer
*
- * - a2 contains the expected sealing type.
- *
- * - t0 holds a copy of the user key's address field (authorized type)
+ * - ca2 holds the unsealing authority and is clobbered on failure
+ * explicitly and on success with a scalar (the sealed payload's length)
*
* - t1 is used within each local computation and never holds secrets
*/
@@ -53,53 +71,41 @@
andi t1, t1, CHERI_PERM_UNSEAL
beqz t1, .Lexit_failure
- /* Copy key type to scratch register */
- cgetaddr t0, ca0
-
- /*
- * Load unsealing root capability, to be clobbered by return value
- * This faults only if something has gone very, very wrong, and exposes no
- * secrets if so.
- */
-.Lload_sealing_key:
- auipcc ca0, %cheriot_compartment_hi(__sealingkey)
- clc ca0, %cheriot_compartment_lo_i(.Lload_sealing_key)(ca0)
- csetaddr ca0, ca0, a2
-
/* Unseal, clobbering authority */
- cunseal ca0, ca1, ca0
+ cunseal ca2, ca1, ca2
/* Verify tag of unsealed form */
- cgettag t1, ca0
+ cgettag t1, ca2
beqz t1, .Lexit_failure
/*
* Load software type tag. This will not trap, thanks to above tag check and
* because IRQs are deferred (see our export entry below)
*/
- clw t1, TokenSObj_offset_type(ca0)
+ clw t1, TokenSObj_offset_type(ca2)
/* Verify that the loaded value matches the address of the key. */
- bne t0, t1, .Lexit_failure
+ bne a0, t1, .Lexit_failure
/* Subset bounds to ->data */
// Get the top into t1
- cgettop t1, ca0
- // Move the address to the start of the data
- cincoffset ca0, ca0, TokenSObj_offset_data
+ cgettop t1, ca2
+ // Move the address to the start of the data, clobber the user's sealing key
+ cincoffset ca0, ca2, TokenSObj_offset_data
// Subtract the address of the (to-be-returned-unsealed) data from the top to
- // give the length.
- sub t1, t1, a0
+ // give the length, clobbering our unsealing key.
+ sub a2, t1, a0
// Set the new bounds, using an exact setting so that any errors in the
// allocator's alignment turn into an untagged capability here.
- csetboundsexact ca0, ca0, t1
+ csetboundsexact ca0, ca0, a2
/* And that's an unwrap. */
cret
.Lexit_failure:
- /* Failure; clobber potential sensitive state in ca0 and return null */
- cmove ca0, cnull
+ /* Failure; clobber potential sensitive state in ca2 and return null */
+ zeroOne a2
+ zeroOne a0
cret
/**
@@ -113,7 +119,16 @@
.hidden _Z16token_obj_unsealP10SKeyStructP10SObjStruct
.globl _Z16token_obj_unsealP10SKeyStructP10SObjStruct
_Z16token_obj_unsealP10SKeyStructP10SObjStruct:
- cgettype a2, ca1
+ LoadCapPCC ca2, __sealingkey_either
+
+ /*
+ * Backwards compatibility with CUnseal that requires address match.
+ * This can (and should) be removed once everyone's caught up with
+ * https://github.com/CHERIoT-Platform/cheriot-sail/pull/87 .
+ */
+ cgettype t1, ca1
+ csetaddr ca2, ca2, t1
+
j .Ltoken_unseal_internal
/**
@@ -127,8 +142,8 @@
.hidden _Z23token_obj_unseal_staticP10SKeyStructP10SObjStruct
.globl _Z23token_obj_unseal_staticP10SKeyStructP10SObjStruct
_Z23token_obj_unseal_staticP10SKeyStructP10SObjStruct:
- li a2, CheriSealTypeStaticToken
- j .Ltoken_unseal_internal
+ LoadCapPCC ca2, __sealingkey_static
+ j .Ltoken_unseal_internal
/**
* An in-assembler implementation of
@@ -138,11 +153,11 @@
*
* The name has been manually mangled as per the C++ rules.
*/
- .hidden _Z16token_obj_unsealP10SKeyStructP10SObjStruct
- .globl _Z16token_obj_unsealP10SKeyStructP10SObjStruct
+ .hidden _Z24token_obj_unseal_dynamicP10SKeyStructP10SObjStruct
+ .globl _Z24token_obj_unseal_dynamicP10SKeyStructP10SObjStruct
_Z24token_obj_unseal_dynamicP10SKeyStructP10SObjStruct:
- li a2, CheriSealTypeAllocator
- j .Ltoken_unseal_internal
+ LoadCapPCC ca2, __sealingkey_dynamic
+ j .Ltoken_unseal_internal
/* TODO: Eventually this goes away, when the assembler can generate it for us */
CHERIOT_EXPORT_LIBCALL \
