[PATCH v1 1/1] aarch64: make RA signing method extendable for upcoming PAuth_LR
Matthieu Longo
matthieu.longo@arm.com
Fri Nov 8 15:25:05 GMT 2024
The Pointer Authentication (PAuth) architecture provides instructions
that enable software to sign an address using SP as a diversifier.
This form of PAC instruction is typically used for signing return
addresses that are stored on the stack.
The new Armv9.5-A architecture introduces an enhancement of the
previous PAuth feature, called PAuth_LR. It aims at hardening the PAC
in a signed return address. When signing the return address in LR, the
PC is used as a diversifier, in addition to the SP to generate PAC code.
PAuth introduced the DWARF register RA_SIGN_STATE which stores the
return address signed state (currently no signing, or signed with SP).
PAuth_LR adds a new value to this state: signed with SP and PC.
This DWARF register can now be set via 2 directives:
- DW_CFA_AARCH64_negate_ra_state: toggle the RA state in a PAuth
context.
- DW_CFA_AARCH64_negate_ra_state_with_pc: toggle the RA state in a
PAuth_LR context.
The existing implementation relies on a binary approach that cannot
accomodate with the new state value.
This patch is a refactoring to make the RA signing method extendable for
the upcoming PAuth_LR patch series.
---
gas/gen-sframe.c | 22 ++++++++++++++--------
gas/gen-sframe.h | 17 ++++++++++++++---
include/sframe.h | 4 ++--
3 files changed, 30 insertions(+), 13 deletions(-)
diff --git a/gas/gen-sframe.c b/gas/gen-sframe.c
index 626dc33b71d..565148d2842 100644
--- a/gas/gen-sframe.c
+++ b/gas/gen-sframe.c
@@ -254,11 +254,13 @@ static struct sframe_version_ops sframe_ver_ops;
static unsigned char
sframe_v1_set_fre_info (unsigned int base_reg, unsigned int num_offsets,
- unsigned int offset_size, bool mangled_ra_p)
+ unsigned int offset_size,
+ ra_signing_method_t ra_signing_info)
{
unsigned char fre_info;
fre_info = SFRAME_V1_FRE_INFO (base_reg, num_offsets, offset_size);
- fre_info = SFRAME_V1_FRE_INFO_UPDATE_MANGLED_RA_P (mangled_ra_p, fre_info);
+ fre_info = SFRAME_V1_FRE_INFO_UPDATE_RA_SIGNING_INFO (ra_signing_info,
+ fre_info);
return fre_info;
}
@@ -292,10 +294,11 @@ sframe_set_version (uint32_t sframe_version ATTRIBUTE_UNUSED)
static unsigned char
sframe_set_fre_info (unsigned int base_reg, unsigned int num_offsets,
- unsigned int offset_size, bool mangled_ra_p)
+ unsigned int offset_size,
+ ra_signing_method_t ra_signing_info)
{
return sframe_ver_ops.set_fre_info (base_reg, num_offsets,
- offset_size, mangled_ra_p);
+ offset_size, ra_signing_info);
}
/* SFrame set func info. */
@@ -526,7 +529,7 @@ output_sframe_row_entry (symbolS *fde_start_addr,
fre_num_offsets = get_fre_num_offsets (sframe_fre);
fre_offset_size = sframe_get_fre_offset_size (sframe_fre);
fre_info = sframe_set_fre_info (fre_base_reg, fre_num_offsets,
- fre_offset_size, sframe_fre->mangled_ra_p);
+ fre_offset_size, sframe_fre->ra_signing_info);
out_one (fre_info);
idx = sframe_fre_offset_func_map_index (fre_offset_size);
@@ -879,7 +882,7 @@ sframe_row_entry_new (void)
fre->merge_candidate = true;
/* Reset the mangled RA status bit to zero by default. We will initialize it in
sframe_row_entry_initialize () with the sticky bit if set. */
- fre->mangled_ra_p = false;
+ fre->ra_signing_info = ra_no_signing;
return fre;
}
@@ -927,7 +930,7 @@ sframe_row_entry_initialize (struct sframe_row_entry *cur_fre,
cur_fre->ra_offset = prev_fre->ra_offset;
/* Treat RA mangling as a sticky bit. It retains its value until another
.cfi_negate_ra_state is seen. */
- cur_fre->mangled_ra_p = prev_fre->mangled_ra_p;
+ cur_fre->ra_signing_info = prev_fre->ra_signing_info;
}
/* Return SFrame register name for SP, FP, and RA, or NULL if other. */
@@ -1276,7 +1279,10 @@ sframe_xlate_do_aarch64_negate_ra_state (struct sframe_xlate_ctx *xlate_ctx,
gas_assert (cur_fre);
/* Toggle the mangled RA status bit. */
- cur_fre->mangled_ra_p = !cur_fre->mangled_ra_p;
+ cur_fre->ra_signing_info
+ = ((cur_fre->ra_signing_info == ra_no_signing)
+ ? ra_signing_sp
+ : ra_no_signing);
cur_fre->merge_candidate = false;
return SFRAME_XLATE_OK;
diff --git a/gas/gen-sframe.h b/gas/gen-sframe.h
index 8ed46dbb087..35cc01ff0be 100644
--- a/gas/gen-sframe.h
+++ b/gas/gen-sframe.h
@@ -21,11 +21,22 @@
#ifndef GENSFRAME_H
#define GENSFRAME_H
+#include "ansidecl.h"
+
#define SFRAME_FRE_ELEM_LOC_REG 0
#define SFRAME_FRE_ELEM_LOC_STACK 1
#define SFRAME_FRE_BASE_REG_INVAL ((unsigned int)-1)
+/* Signing method used for return address authentication.
+ (AArch64 extension) */
+
+typedef enum ATTRIBUTE_PACKED
+{
+ ra_no_signing = 0x0,
+ ra_signing_sp = 0x1,
+} ra_signing_method_t;
+
/* SFrame Frame Row Entry (FRE).
A frame row entry is a slice of the frame and can be valid for a set of
@@ -52,8 +63,8 @@ struct sframe_row_entry
on it. */
bool merge_candidate;
- /* Whether the return address is mangled with pauth code. */
- bool mangled_ra_p;
+ /* Track the PAuth mangling information for RA. */
+ ra_signing_method_t ra_signing_info;
/* Track CFA base (architectural) register ID. */
unsigned int cfa_base_reg;
@@ -146,7 +157,7 @@ struct sframe_version_ops
unsigned char format_version; /* SFrame format version. */
/* set SFrame FRE info. */
unsigned char (*set_fre_info) (unsigned int, unsigned int, unsigned int,
- bool);
+ ra_signing_method_t);
/* set SFrame Func info. */
unsigned char (*set_func_info) (unsigned int, unsigned int, unsigned int);
};
diff --git a/include/sframe.h b/include/sframe.h
index 347dbc73787..4e7092d0bbe 100644
--- a/include/sframe.h
+++ b/include/sframe.h
@@ -264,8 +264,8 @@ typedef struct sframe_fre_info
(((offset_num) & 0xf) << 1) | ((base_reg_id) & 0x1))
/* Set the mangled_ra_p bit as indicated. */
-#define SFRAME_V1_FRE_INFO_UPDATE_MANGLED_RA_P(mangled_ra_p, fre_info) \
- ((((mangled_ra_p) & 0x1) << 7) | ((fre_info) & 0x7f))
+#define SFRAME_V1_FRE_INFO_UPDATE_RA_SIGNING_INFO(ra_signing_info, fre_info) \
+ ((((ra_signing_info) & 0x1) << 7) | ((fre_info) & 0x7f))
#define SFRAME_V1_FRE_CFA_BASE_REG_ID(data) ((data) & 0x1)
#define SFRAME_V1_FRE_OFFSET_COUNT(data) (((data) >> 1) & 0xf)
--
2.47.0
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