2023-10-04 15:16:06

by Clément Léger

Subject: [PATCH v2 8/8] riscv: add support for PR_SET_UNALIGN and PR_GET_UNALIGN

Now that trap support is ready to handle misalignment errors in S-mode,
allow the user to control the behavior of misaligned accesses using
prctl(PR_SET_UNALIGN). Add an align_ctl flag in thread_struct which
will be used to determine if we should SIGBUS the process or not on
such fault.

Signed-off-by: Clément Léger <[email protected]>
---
arch/riscv/include/asm/processor.h | 9 +++++++++
arch/riscv/kernel/process.c | 18 ++++++++++++++++++
arch/riscv/kernel/traps_misaligned.c | 6 ++++++
3 files changed, 33 insertions(+)

diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 3e23e1786d05..adbe520d07c5 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -8,6 +8,7 @@

#include <linux/const.h>
#include <linux/cache.h>
+#include <linux/prctl.h>

#include <vdso/processor.h>

@@ -82,6 +83,7 @@ struct thread_struct {
unsigned long bad_cause;
unsigned long vstate_ctrl;
struct __riscv_v_ext_state vstate;
+ unsigned long align_ctl;
};

/* Whitelist the fstate from the task_struct for hardened usercopy */
@@ -94,6 +96,7 @@ static inline void arch_thread_struct_whitelist(unsigned long *offset,

#define INIT_THREAD { \
.sp = sizeof(init_stack) + (long)&init_stack, \
+ .align_ctl = PR_UNALIGN_NOPRINT, \
}

#define task_pt_regs(tsk) \
@@ -134,6 +137,12 @@ extern long riscv_v_vstate_ctrl_set_current(unsigned long arg);
extern long riscv_v_vstate_ctrl_get_current(void);
#endif /* CONFIG_RISCV_ISA_V */

+extern int get_unalign_ctl(struct task_struct *tsk, unsigned long addr);
+extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
+
+#define GET_UNALIGN_CTL(tsk, addr) get_unalign_ctl((tsk), (addr))
+#define SET_UNALIGN_CTL(tsk, val) set_unalign_ctl((tsk), (val))
+
#endif /* __ASSEMBLY__ */

#endif /* _ASM_RISCV_PROCESSOR_H */
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index e32d737e039f..4f21d970a129 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -25,6 +25,7 @@
#include <asm/thread_info.h>
#include <asm/cpuidle.h>
#include <asm/vector.h>
+#include <asm/cpufeature.h>

register unsigned long gp_in_global __asm__("gp");

@@ -41,6 +42,23 @@ void arch_cpu_idle(void)
cpu_do_idle();
}

+int set_unalign_ctl(struct task_struct *tsk, unsigned int val)
+{
+ if (!unaligned_ctl_available())
+ return -EINVAL;
+
+ tsk->thread.align_ctl = val;
+ return 0;
+}
+
+int get_unalign_ctl(struct task_struct *tsk, unsigned long adr)
+{
+ if (!unaligned_ctl_available())
+ return -EINVAL;
+
+ return put_user(tsk->thread.align_ctl, (unsigned long __user *)adr);
+}
+
void __show_regs(struct pt_regs *regs)
{
show_regs_print_info(KERN_DEFAULT);
diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
index d99b95084b6c..bba301b5194d 100644
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -418,6 +418,9 @@ int handle_misaligned_load(struct pt_regs *regs)
if (!unaligned_enabled)
return -1;

+ if (user_mode(regs) && (current->thread.align_ctl & PR_UNALIGN_SIGBUS))
+ return -1;
+
if (get_insn(regs, epc, &insn))
return -1;

@@ -517,6 +520,9 @@ int handle_misaligned_store(struct pt_regs *regs)
if (!unaligned_enabled)
return -1;

+ if (user_mode(regs) && (current->thread.align_ctl & PR_UNALIGN_SIGBUS))
+ return -1;
+
if (get_insn(regs, epc, &insn))
return -1;

--
2.42.0

2023-10-04 17:20:00

by Björn Töpel

Subject: Re: [PATCH v2 8/8] riscv: add support for PR_SET_UNALIGN and PR_GET_UNALIGN

Clément Léger <[email protected]> writes:

> Now that trap support is ready to handle misalignment errors in S-mode,
> allow the user to control the behavior of misaligned accesses using
> prctl(PR_SET_UNALIGN). Add an align_ctl flag in thread_struct which
> will be used to determine if we should SIGBUS the process or not on
> such fault.
>
> Signed-off-by: Clément Léger <[email protected]>

Reviewed-by: Björn Töpel <[email protected]>