![]() 32-bit user code that uses int $80 doesn't care about r8-r11. There is, however, some 64-bit user code that intentionally uses int $0x80 to invoke 32-bit system calls. From what I've seen, basically all such code assumes that r8-r15 are all preserved, but the kernel clobbers r8-r11. Since I doubt that there's any code that depends on int $0x80 zeroing r8-r11, change the kernel to preserve them. I suspect that very little user code is broken by the old clobber, since r8-r11 are only rarely allocated by gcc, and they're clobbered by function calls, so they only way we'd see a problem is if the same function that invokes int $0x80 also spills something important to one of these registers. The current behavior seems to date back to the historical commit "[PATCH] x86-64 merge for 2.6.4". Before that, all regs were preserved. I can't find any explanation of why this change was made. Update the test_syscall_vdso_32 testcase as well to verify the new behavior, and it strengthens the test to make sure that the kernel doesn't accidentally permute r8..r15. Suggested-by: Denys Vlasenko <dvlasenk@redhat.com> Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Dominik Brodowski <linux@dominikbrodowski.net> Link: https://lkml.kernel.org/r/d4c4d9985fbe64f8c9e19291886453914b48caee.1523975710.git.luto@kernel.org |
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bpf | ||
breakpoints | ||
capabilities | ||
cpu-hotplug | ||
cpufreq | ||
drivers/gpu | ||
efivarfs | ||
exec | ||
filesystems | ||
firmware | ||
ftrace | ||
futex | ||
gpio | ||
ia64 | ||
intel_pstate | ||
ipc | ||
kcmp | ||
kmod | ||
kvm | ||
lib | ||
locking | ||
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membarrier | ||
memfd | ||
memory-hotplug | ||
mount | ||
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net | ||
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ntb | ||
powerpc | ||
prctl | ||
proc | ||
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ptrace | ||
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size | ||
splice | ||
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kselftest_harness.h | ||
kselftest_install.sh | ||
lib.mk | ||
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