@@ -13,6 +13,7 @@
#include <asm/traps.h>
#include "simulate-insn.h"
+#include "asm/gcs.h"
#define bbl_displacement(insn) \
sign_extend32(((insn) & 0x3ffffff) << 2, 27)
@@ -49,6 +50,18 @@ static inline u32 get_w_reg(struct pt_regs *regs, int reg)
return lower_32_bits(pt_regs_read_reg(regs, reg));
}
+static inline void update_lr(struct pt_regs *regs, long addr)
+{
+ int err = 0;
+
+ if (user_mode(regs) && task_gcs_el0_enabled(current)) {
+ push_user_gcs(addr + 4, &err);
+ if (err)
+ force_sig(SIGSEGV);
+ }
+ procedure_link_pointer_set(regs, addr + 4);
+}
+
static bool __kprobes check_cbz(u32 opcode, struct pt_regs *regs)
{
int xn = opcode & 0x1f;
@@ -107,9 +120,8 @@ simulate_b_bl(u32 opcode, long addr, struct pt_regs *regs)
{
int disp = bbl_displacement(opcode);
- /* Link register is x30 */
if (opcode & (1 << 31))
- set_x_reg(regs, 30, addr + 4);
+ update_lr(regs, addr);
instruction_pointer_set(regs, addr + disp);
}
@@ -133,17 +145,25 @@ simulate_br_blr(u32 opcode, long addr, struct pt_regs *regs)
/* update pc first in case we're doing a "blr lr" */
instruction_pointer_set(regs, get_x_reg(regs, xn));
- /* Link register is x30 */
if (((opcode >> 21) & 0x3) == 1)
- set_x_reg(regs, 30, addr + 4);
+ update_lr(regs, addr);
}
void __kprobes
simulate_ret(u32 opcode, long addr, struct pt_regs *regs)
{
+ u64 ret_addr;
+ int err = 0;
int xn = (opcode >> 5) & 0x1f;
instruction_pointer_set(regs, get_x_reg(regs, xn));
+
+ if (user_mode(regs) && task_gcs_el0_enabled(current)) {
+ ret_addr = pop_user_gcs(&err);
+ if (err || ret_addr != procedure_link_pointer(regs))
+ force_sig(SIGSEGV);
+ }
+
}
void __kprobes
The arm64 probe simulation doesn't currently have logic in place to deal with GCS and this results in core dumps if probes are inserted at control flow locations. Fix-up bl, blr and ret to manipulate the shadow stack as needed. While we manipulate and validate the shadow stack correctly, the hardware provides additional security by only allowing GCS operations against pages which are marked to support GCS. For writing there is gcssttr() which enforces this, but there isn't an equivalent for reading. This means that uprobe users should be aware that probing on control flow instructions which require reading the shadow stack (ex: ret) offers lower security guarantees than what is achieved without the uprobe active. Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> --- arch/arm64/kernel/probes/simulate-insn.c | 28 ++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-)