Messages in this thread | | | Date | Mon, 3 Apr 2023 17:21:27 +0100 | From | Conor Dooley <> | Subject | Re: [PATCH] riscv: entry: Save a0 prior syscall_enter_from_user_mode() |
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On Mon, Apr 03, 2023 at 08:52:07AM +0200, Björn Töpel wrote: > From: Björn Töpel <bjorn@rivosinc.com> > > The RISC-V calling convention passes the first argument, and the > return value in the a0 register. For this reason, the a0 register > needs some extra care; When handling syscalls, the a0 register is > saved into regs->orig_a0, so a0 can be properly restored for, > e.g. interrupted syscalls. > > This functionality was broken with the introduction of the generic > entry patches. Here, a0 was saved into orig_a0 after calling > syscall_enter_from_user_mode(), which can change regs->a0 for some > paths, incorrectly restoring a0. > > This is resolved, by saving a0 prior doing the > syscall_enter_from_user_mode() call. > > Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry") > Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu> > Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu> > Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
As you pointed out, v12 did indeed have this ordering, so *deep breath* Reported-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/linux-riscv/60ee7c26-1a70-427d-beaf-92e2989fc479@spud/ Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Tested-by: Conor Dooley <conor.dooley@microchip.com>
Thanks for fixing this Björn! > --- > arch/riscv/kernel/traps.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c > index 1f4e37be7eb3..8c258b78c925 100644 > --- a/arch/riscv/kernel/traps.c > +++ b/arch/riscv/kernel/traps.c > @@ -270,11 +270,11 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) > if (user_mode(regs)) { > ulong syscall = regs->a7; > > - syscall = syscall_enter_from_user_mode(regs, syscall); > - > regs->epc += 4; > regs->orig_a0 = regs->a0; > > + syscall = syscall_enter_from_user_mode(regs, syscall); > + > if (syscall < NR_syscalls) > syscall_handler(regs, syscall); > else > > base-commit: d34a6b715a23ccd9c9d0bc7a475bea59dc3e28b2 > -- > 2.37.2 > [unhandled content-type:application/pgp-signature] | |