On Sat, Jan 27, 2024 at 05:05:57AM +0800, Xi Ruoyao wrote:
> If we still own the FPU after initializing fcr31, when we are preempted
> the dirty value in the FPU will be read out and stored into fcr31,
> clobbering our setting. This can cause an improper floating-point
> environment after execve(). For example:
>
> zsh% cat measure.c
> #include <fenv.h>
> int main() { return fetestexcept(FE_INEXACT); }
> zsh% cc measure.c -o measure -lm
> zsh% echo $((1.0/3)) # raising FE_INEXACT
> 0.33333333333333331
> zsh% while ./measure; do ; done
> (stopped in seconds)
>
> Call lose_fpu(0) before setting fcr31 to prevent this.
>
> Closes: https://lore.kernel.org/linux-mips/7a6aa1bbdbbe2e63ae96ff163fab0349f58f1b9e.camel@xxxxxxxxxxx/
> Fixes: 9b26616c8d9d ("MIPS: Respect the ISA level in FCSR handling")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
> ---
>
> v1 -> v2: Fix stable list address in Cc line.
>
> arch/mips/kernel/elf.c | 6 ++++++
> 1 file changed, 6 insertions(+)
applied to mips-fixes.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
