Re: [PATCH v4 15/29] arm64: handle PKEY/POE faults

On Thu, Jul 25, 2024 at 04:57:09PM +0100, Dave Martin wrote:

On Fri, May 03, 2024 at 02:01:33PM +0100, Joey Gouly wrote:

quoted

If a memory fault occurs that is due to an overlay/pkey fault, report that to
userspace with a SEGV_PKUERR.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/traps.h |  1 +
 arch/arm64/kernel/traps.c      | 12 ++++++--
 arch/arm64/mm/fault.c          | 56 ++++++++++++++++++++++++++++++++--
 3 files changed, 64 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
index eefe766d6161..f6f6f2cb7f10 100644
--- a/arch/arm64/include/asm/traps.h
+++ b/arch/arm64/include/asm/traps.h

@@ -25,6 +25,7 @@ try_emulate_armv8_deprecated(struct pt_regs *regs, u32 insn)
 void force_signal_inject(int signal, int code, unsigned long address, unsigned long err);
 void arm64_notify_segfault(unsigned long addr);
 void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *str);
+void arm64_force_sig_fault_pkey(int signo, int code, unsigned long far, const char *str, int pkey);
 void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str);
 void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str);
 

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 215e6d7f2df8..1bac6c84d3f5 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c

@@ -263,16 +263,24 @@ static void arm64_show_signal(int signo, const char *str)
 	__show_regs(regs);
 }
 
-void arm64_force_sig_fault(int signo, int code, unsigned long far,
-			   const char *str)
+void arm64_force_sig_fault_pkey(int signo, int code, unsigned long far,
+			   const char *str, int pkey)
 {
 	arm64_show_signal(signo, str);
 	if (signo == SIGKILL)
 		force_sig(SIGKILL);
+	else if (code == SEGV_PKUERR)
+		force_sig_pkuerr((void __user *)far, pkey);

Is signo definitely SIGSEGV here?  It looks to me like we can get in
here for SIGBUS, SIGTRAP etc.

si_codes are not unique between different signo here, so I'm wondering
whether this should this be:

	else if (signo == SIGSEGV && code == SEGV_PKUERR)

...?

quoted

 	else
 		force_sig_fault(signo, code, (void __user *)far);
 }
 
+void arm64_force_sig_fault(int signo, int code, unsigned long far,
+			   const char *str)
+{
+	arm64_force_sig_fault_pkey(signo, code, far, str, 0);

Is there a reason not to follow the same convention as elsewhere, where
-1 is passed for "no pkey"?

If we think this should never be called with signo == SIGSEGV &&
code == SEGV_PKUERR and no valid pkey but if it's messy to prove, then
maybe a WARN_ON_ONCE() would be worth it here?

Anshuman suggested to separate them out, which I did like below, I think that
addresses your comments too?

diff --git arch/arm64/kernel/traps.c arch/arm64/kernel/traps.c
index 215e6d7f2df8..49bac9ae04c0 100644
--- arch/arm64/kernel/traps.c
+++ arch/arm64/kernel/traps.c

@@ -273,6 +273,13 @@ void arm64_force_sig_fault(int signo, int code, unsigned long far,
                force_sig_fault(signo, code, (void __user *)far);
 }
 
+void arm64_force_sig_fault_pkey(int signo, int code, unsigned long far,
+                          const char *str, int pkey)
+{
+       arm64_show_signal(signo, str);
+       force_sig_pkuerr((void __user *)far, pkey);
+}
+
 void arm64_force_sig_mceerr(int code, unsigned long far, short lsb,
                            const char *str)
 {

diff --git arch/arm64/mm/fault.c arch/arm64/mm/fault.c
index 451ba7cbd5ad..1ddd46b97f88 100644
--- arch/arm64/mm/fault.c
+++ arch/arm64/mm/fault.c

-               arm64_force_sig_fault(SIGSEGV, si_code, far, inf->name);
+               if (si_code == SEGV_PKUERR)
+                       arm64_force_sig_fault_pkey(SIGSEGV, si_code, far, inf->name, pkey);
+               else
+                       arm64_force_sig_fault(SIGSEGV, si_code, far, inf->name);

Thanks,
Joey