riscv, mm: Perform BPF exhandler fixup on page fault

commit 416721ff05fddc58ca531b6f069de250301de6e5 upstream.

Commit 21855cac82d3 ("riscv/mm: Prevent kernel module to access user
memory without uaccess routines") added early exits/deaths for page
faults stemming from accesses to user-space without using proper
uaccess routines (where sstatus.SUM is set).

Unfortunatly, this is too strict for some BPF programs, which relies
on BPF exhandler fixups. These BPF programs loads "BTF pointers". A
BTF pointers could either be a valid kernel pointer or NULL, but not a
userspace address.

Resolve the problem by calling the fixup handler in the early exit
path.

Fixes: 21855cac82d3 ("riscv/mm: Prevent kernel module to access user memory without uaccess routines")
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20230214162515.184827-1-bjorn@kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 676a3f28811fade45dcc963acfc39505e70128ac..884a3c76573cf50980c52a6fdae10603b04b45c6 100644 (file)
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -271,10 +271,12 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;
 
-       if (!user_mode(regs) && addr < TASK_SIZE &&
-                       unlikely(!(regs->status & SR_SUM)))
-               die_kernel_fault("access to user memory without uaccess routines",
-                               addr, regs);
+       if (!user_mode(regs) && addr < TASK_SIZE && unlikely(!(regs->status & SR_SUM))) {
+               if (fixup_exception(regs))
+                       return;
+
+               die_kernel_fault("access to user memory without uaccess routines", addr, regs);
+       }
 
        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);