On Tue, Sep 8, 2020 at 2:17 AM Sean Anderson <sean...@gmail.com> wrote: > > 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
nits: wrong fixes tag format > Signed-off-by: Sean Anderson <sean...@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 This is currently in the #ifndef CONFIG_XIP block. Should consider the #else branch? > + > /* 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); > > -- Regards, Bin