[PATCH 6/7] riscv: Ensure gp is NULL or points to valid data
Sean Anderson
seanga2 at gmail.com
Mon Sep 7 20:16:58 CEST 2020
This allows code to use a construct like `if (gd & gd->...) { ... }` when
accessing the global data pointer. Without this change, it was possible for
a very early trap to cause _exit_trap to read arbitrary memory. This could
cause a second trap, preventing show_regs from being printed.
Fixes: 7c6ca03eaed0035ca6676e9bc7f5f1dfcaae7e8f
Signed-off-by: Sean Anderson <seanga2 at gmail.com>
---
arch/riscv/cpu/start.S | 20 +++++++++++++++++---
arch/riscv/lib/interrupts.c | 3 ++-
2 files changed, 19 insertions(+), 4 deletions(-)
diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index ad18e746b6..59d3d7bbf4 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -47,6 +47,13 @@ _start:
mv tp, a0
mv s1, a1
+ /*
+ * Set the global data pointer to a known value in case we get a very
+ * early trap. The global data pointer will be set its actual value only
+ * after it has been initialized.
+ */
+ mv gp, zero
+
la t0, trap_entry
csrw MODE_PREFIX(tvec), t0
@@ -85,10 +92,10 @@ call_board_init_f_0:
jal board_init_f_alloc_reserve
/*
- * Set global data pointer here for all harts, uninitialized at this
- * point.
+ * Save global data pointer for later. We don't set it here because it
+ * is not initialized yet.
*/
- mv gp, a0
+ mv s0, a0
/* setup stack */
#if CONFIG_IS_ENABLED(SMP)
@@ -135,6 +142,13 @@ wait_for_gd_init:
fence r, rw
bnez t1, 1b
+ /*
+ * Set the global data pointer only when gd_t has been initialized.
+ * This was already set by arch_setup_gd on the boot hart, but all other
+ * harts' global data pointers gets set here.
+ */
+ mv gp, s0
+
/* register available harts in the available_harts mask */
li t1, 1
sll t1, t1, tp
diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c
index cd47e64487..ad870e98d8 100644
--- a/arch/riscv/lib/interrupts.c
+++ b/arch/riscv/lib/interrupts.c
@@ -78,7 +78,8 @@ static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs)
printf("EPC: " REG_FMT " RA: " REG_FMT " TVAL: " REG_FMT "\n",
epc, regs->ra, tval);
- if (gd->flags & GD_FLG_RELOC)
+ /* Print relocation adjustments, but only if gd is initialized */
+ if (gd && gd->flags & GD_FLG_RELOC)
printf("EPC: " REG_FMT " RA: " REG_FMT " reloc adjusted\n\n",
epc - gd->reloc_off, regs->ra - gd->reloc_off);
--
2.28.0
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