From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Anderson Date: Mon, 7 Sep 2020 14:16:58 -0400 Subject: [PATCH 6/7] riscv: Ensure gp is NULL or points to valid data In-Reply-To: <20200907181659.92449-1-seanga2@gmail.com> References: <20200907181659.92449-1-seanga2@gmail.com> Message-ID: <20200907181659.92449-7-seanga2@gmail.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de 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 --- 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