BMC/Intel-BMC/linux.git/arch/x86/kernel/fpu/core.c, branch dev

x86/fpu/math-emu: Fix crash in fork()

2015-08-22T08:23:03+00:00

During later stages of math-emu bootup the following crash triggers: math_emulate: 0060:c100d0a8 Kernel panic - not syncing: Math emulation needed in kernel CPU: 0 PID: 1511 Comm: login Not tainted 4.2.0-rc7+ #1012 [...] Call Trace: [] dump_stack+0x41/0x52 [] panic+0x77/0x189 [] ? math_error+0x140/0x140 [] math_emulate+0xba7/0xbd0 [] ? fpu__copy+0x138/0x1c0 [] ? __alloc_pages_nodemask+0x12c/0x870 [] ? proc_clear_tty+0x40/0x70 [] ? session_clear_tty+0x1e/0x30 [] ? math_error+0x140/0x140 [] do_device_not_available+0x45/0x70 [] ? fpu__copy+0x138/0x1c0 [] error_code+0x5a/0x60 [] ? math_error+0x140/0x140 [] ? fpu__copy+0x138/0x1c0 [] arch_dup_task_struct+0x25/0x30 [] copy_process.part.51+0xea/0x1480 [] ? dput+0x175/0x200 [] ? no_tty+0x30/0x30 [] ? do_vfs_ioctl+0x322/0x540 [] _do_fork+0xca/0x340 [] ? SyS_rt_sigaction+0x66/0x90 [] SyS_clone+0x27/0x30 [] sysenter_do_call+0x12/0x12 The reason is the incorrect assumption in fpu_copy(), that FNSAVE can be executed from math-emu kernels as well. Don't try to copy the registers, the soft state will be copied by fork anyway, so the child task inherits the parent task's soft math state. With this fix applied math-emu kernels boot up fine on modern hardware and the 'no387 nofxsr' boot options. Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Denys Vlasenko Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Quentin Casasnovas Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Standardize the parameter type of copy_kernel_to_fpregs()

2015-05-27T12:11:32+00:00

Bring the __copy_fpstate_to_fpregs() and copy_fpstate_to_fpregs() functions in line with the parameter passing convention of other kernel-to-FPU-registers copying functions: pass around an in-memory FPU register state pointer, instead of struct fpu *. NOTE: This patch also changes the assembly constraint of the FXSAVE-leak workaround from 'fpu->fpregs_active' to 'fpstate' - but that is fine, as we only need a valid memory address there for the FILDL instruction. Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Remove error return values from copy_kernel_to_*regs() functions

2015-05-27T12:11:30+00:00

None of the copy_kernel_to_*regs() FPU register copying functions are supposed to fail, and all of them have debugging checks that enforce this. Remove their return values and simplify their call sites, which have redundant error checks and error handling code paths. Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Rename copy_fpstate_to_fpregs() to copy_kernel_to_fpregs()

2015-05-27T12:11:29+00:00

Bring the __copy_fpstate_to_fpregs() and copy_fpstate_to_fpregs() functions in line with the naming of other kernel-to-FPU-registers copying functions. Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Add debugging check to fpu__restore()

2015-05-27T12:11:27+00:00

The copy_fpstate_to_fpregs() function is never supposed to fail, so add a debugging check to its call site in fpu__restore(). Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Optimize fpu__activate_fpstate_write()

2015-05-27T12:11:27+00:00

fpu__activate_fpstate_write() is used before ptrace writes to the fpstate context. Because it expects the modified registers to be reloaded on the nexts context switch, it's only valid to call this function for stopped child tasks. - add a debugging check for this assumption - remove code that only runs if the current task's FPU state needs to be saved, which cannot occur here - update comments to match the implementation Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Rename fpu__activate_fpstate() to fpu__activate_fpstate_write()

2015-05-27T12:11:26+00:00

Remaining users of fpu__activate_fpstate() are all places that want to modify FPU registers, rename the function to fpu__activate_fpstate_write() according to this usage. Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Optimize fpu__activate_fpstate_read()

2015-05-27T12:11:25+00:00

fpu__activate_fpstate_read() is used before FPU registers are read from the fpstate by ptrace and core dumping. It's not necessary to unlazy non-current child tasks in this case, since the reading of registers is non-destructive. Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Split out the fpu__activate_fpstate_read() method

2015-05-27T12:11:24+00:00

Currently fpu__activate_fpstate() is used for two distinct purposes: - read access by ptrace and core dumping, where in the core dumping case the current task's FPU state may be examined as well. - write access by ptrace, which modifies FPU registers and expects the modified registers to be reloaded on the next context switch. Split out the reading side into fpu__activate_fpstate_read(). ( Note that this is just a pure duplication of fpu__activate_fpstate() for the time being, we'll optimize the new function in the next patch. ) Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Fix FPU register read access to the current task

2015-05-27T10:40:18+00:00

Bobby Powers reported the following FPU warning during ELF coredumping: WARNING: CPU: 0 PID: 27452 at arch/x86/kernel/fpu/core.c:324 fpu__activate_stopped+0x8a/0xa0() This warning unearthed an invalid assumption about fpu__activate_stopped() that I added in: 67e97fc2ec57 ("x86/fpu: Rename init_fpu() to fpu__unlazy_stopped() and add debugging check") the old init_fpu() function had an (intentional but obscure) side effect: when FPU registers are accessed for the current task, for reading, then it synchronized live in-register FPU state with the fpstate by saving it. So fix this bug by saving the FPU if we are the current task. We'll still warn in fpu__save() if this is called for not yet stopped child tasks, so the debugging check is still preserved. Also rename the function to fpu__activate_fpstate(), because it's not exclusively used for stopped tasks, but for the current task as well. ( Note that this bug calls for a cleaner separation of access-for-read and access-for-modification FPU methods, but we'll do that in separate patches. ) Reported-by: Bobby Powers Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar