[v4] riscv: Discard vector state on syscalls
Commit Message
From: Björn Töpel <bjorn@rivosinc.com>
The RISC-V vector specification states:
Executing a system call causes all caller-saved vector registers
(v0-v31, vl, vtype) and vstart to become unspecified.
The vector registers are set to all 1s, vill is set (invalid), and the
vector status is set to Dirty.
That way we can prevent userspace from accidentally relying on the
stated save.
Rémi pointed out [1] that writing to the registers might be
superfluous, and setting vill is sufficient.
Link: https://lore.kernel.org/linux-riscv/12784326.9UPPK3MAeB@basile.remlab.net/ # [1]
Suggested-by: Darius Rad <darius@bluespec.com>
Suggested-by: Palmer Dabbelt <palmer@rivosinc.com>
Suggested-by: Rémi Denis-Courmont <remi@remlab.net>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
---
v3->v4:
Fixed build CONFIG_RISCV_ISA_V=n builds (Conor)
v2->v3:
Set state to Dirty after discard, for proper ptrace() handling
(Andy)
v1->v2:
Proper register restore for initial state (Andy)
Set registers to 1s, and not 0s (Darius)
---
arch/riscv/include/asm/vector.h | 34 +++++++++++++++++++++++++++++++++
arch/riscv/kernel/traps.c | 2 ++
2 files changed, 36 insertions(+)
base-commit: 488833ccdcac118da16701f4ee0673b20ba47fe3
Comments
On Thu, Jun 29, 2023 at 10:22 PM Björn Töpel <bjorn@kernel.org> wrote:
>
> From: Björn Töpel <bjorn@rivosinc.com>
>
> The RISC-V vector specification states:
> Executing a system call causes all caller-saved vector registers
> (v0-v31, vl, vtype) and vstart to become unspecified.
>
> The vector registers are set to all 1s, vill is set (invalid), and the
> vector status is set to Dirty.
>
> That way we can prevent userspace from accidentally relying on the
> stated save.
>
> Rémi pointed out [1] that writing to the registers might be
> superfluous, and setting vill is sufficient.
>
> Link: https://lore.kernel.org/linux-riscv/12784326.9UPPK3MAeB@basile.remlab.net/ # [1]
> Suggested-by: Darius Rad <darius@bluespec.com>
> Suggested-by: Palmer Dabbelt <palmer@rivosinc.com>
> Suggested-by: Rémi Denis-Courmont <remi@remlab.net>
> Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Thanks,
Reviewed-by: Andy Chiu <andy.chiu@sifive.com>
On Thu, 29 Jun 2023 16:22:28 +0200, Björn Töpel wrote:
> The RISC-V vector specification states:
> Executing a system call causes all caller-saved vector registers
> (v0-v31, vl, vtype) and vstart to become unspecified.
>
> The vector registers are set to all 1s, vill is set (invalid), and the
> vector status is set to Dirty.
>
> [...]
Applied, thanks!
[1/1] riscv: Discard vector state on syscalls
https://git.kernel.org/palmer/c/9657e9b7d253
Best regards,
Hello:
This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:
On Thu, 29 Jun 2023 16:22:28 +0200 you wrote:
> From: Björn Töpel <bjorn@rivosinc.com>
>
> The RISC-V vector specification states:
> Executing a system call causes all caller-saved vector registers
> (v0-v31, vl, vtype) and vstart to become unspecified.
>
> The vector registers are set to all 1s, vill is set (invalid), and the
> vector status is set to Dirty.
>
> [...]
Here is the summary with links:
- [v4] riscv: Discard vector state on syscalls
https://git.kernel.org/riscv/c/9657e9b7d253
You are awesome, thank you!
@@ -33,6 +33,11 @@ static inline void __riscv_v_vstate_clean(struct pt_regs *regs)
regs->status = (regs->status & ~SR_VS) | SR_VS_CLEAN;
}
+static inline void __riscv_v_vstate_dirty(struct pt_regs *regs)
+{
+ regs->status = (regs->status & ~SR_VS) | SR_VS_DIRTY;
+}
+
static inline void riscv_v_vstate_off(struct pt_regs *regs)
{
regs->status = (regs->status & ~SR_VS) | SR_VS_OFF;
@@ -128,6 +133,34 @@ static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_
riscv_v_disable();
}
+static inline void __riscv_v_vstate_discard(void)
+{
+ unsigned long vl, vtype_inval = 1UL << (BITS_PER_LONG - 1);
+
+ riscv_v_enable();
+ asm volatile (
+ ".option push\n\t"
+ ".option arch, +v\n\t"
+ "vsetvli %0, x0, e8, m8, ta, ma\n\t"
+ "vmv.v.i v0, -1\n\t"
+ "vmv.v.i v8, -1\n\t"
+ "vmv.v.i v16, -1\n\t"
+ "vmv.v.i v24, -1\n\t"
+ "vsetvl %0, x0, %1\n\t"
+ ".option pop\n\t"
+ : "=&r" (vl) : "r" (vtype_inval) : "memory");
+ riscv_v_disable();
+}
+
+static inline void riscv_v_vstate_discard(struct pt_regs *regs)
+{
+ if ((regs->status & SR_VS) == SR_VS_OFF)
+ return;
+
+ __riscv_v_vstate_discard();
+ __riscv_v_vstate_dirty(regs);
+}
+
static inline void riscv_v_vstate_save(struct task_struct *task,
struct pt_regs *regs)
{
@@ -173,6 +206,7 @@ static inline bool riscv_v_first_use_handler(struct pt_regs *regs) { return fals
static inline bool riscv_v_vstate_query(struct pt_regs *regs) { return false; }
static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return false; }
#define riscv_v_vsize (0)
+#define riscv_v_vstate_discard(regs) do {} while (0)
#define riscv_v_vstate_save(task, regs) do {} while (0)
#define riscv_v_vstate_restore(task, regs) do {} while (0)
#define __switch_to_vector(__prev, __next) do {} while (0)
@@ -296,6 +296,8 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
regs->epc += 4;
regs->orig_a0 = regs->a0;
+ riscv_v_vstate_discard(regs);
+
syscall = syscall_enter_from_user_mode(regs, syscall);
if (syscall < NR_syscalls)