[PATCH] Ensure predictable endian state on signal handler entry

[PATCH] Ensure predictable endian state on signal handler entry

[Russell King - ARM Linux]

Ensure a predictable endian state when entering signal handlers.  This
avoids programs which use SETEND to momentarily switch their endian
state from having their signal handlers entered with an unpredictable
endian state.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
--

 arch/arm/kernel/signal.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 907d5a6..abaf844 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -474,7 +474,9 @@ setup_return(struct pt_regs *regs, struct k_sigaction *ka,
 	unsigned long handler = (unsigned long)ka->sa.sa_handler;
 	unsigned long retcode;
 	int thumb = 0;
-	unsigned long cpsr = regs->ARM_cpsr & ~PSR_f;
+	unsigned long cpsr = regs->ARM_cpsr & ~(PSR_f | PSR_E_BIT);
+
+	cpsr |= PSR_ENDSTATE;
 
 	/*
 	 * Maybe we need to deliver a 32-bit signal to a 26-bit task.

[PATCH] Ensure predictable endian state on signal handler entry

[Dave Martin]

On Mon, Feb 14, 2011 at 08:02:22PM +0000, Russell King - ARM Linux wrote:
> Ensure a predictable endian state when entering signal handlers.  This
> avoids programs which use SETEND to momentarily switch their endian
> state from having their signal handlers entered with an unpredictable
> endian state.
> 
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> --
> 
>  arch/arm/kernel/signal.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
> index 907d5a6..abaf844 100644
> --- a/arch/arm/kernel/signal.c
> +++ b/arch/arm/kernel/signal.c
> @@ -474,7 +474,9 @@ setup_return(struct pt_regs *regs, struct k_sigaction *ka,
>  	unsigned long handler = (unsigned long)ka->sa.sa_handler;
>  	unsigned long retcode;
>  	int thumb = 0;
> -	unsigned long cpsr = regs->ARM_cpsr & ~PSR_f;
> +	unsigned long cpsr = regs->ARM_cpsr & ~(PSR_f | PSR_E_BIT);
> +
> +	cpsr |= PSR_ENDSTATE;
>  
>  	/*
>  	 * Maybe we need to deliver a 32-bit signal to a 26-bit task.
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Looks sensible to me.

Acked-by: Dave Martin <dave.martin@linaro.org>

Only tested it with little-endian, but it's enough to make my silly
test program not segfault.  (Without your patch, it definitely does...)

#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>

static void handler(int n)
{
	unsigned long cpsr;
#define FORMAT "handler: CPSR = 0x%08lX\n"
	char buf[sizeof FORMAT - 5 + 8];

	asm ("mrs %0, CPSR" : "=r" (cpsr));

	snprintf(buf, sizeof buf, FORMAT, cpsr);

	write(STDOUT_FILENO, buf, strlen(buf));
}

int main(void)
{
	signal(SIGINT, handler);

	asm volatile (
	"0:	setend	be\n\t"
	"	b 0b"
	);
}

Cheers
---Dave