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x86/stackframe/32: Provide consistent pt_regs

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Currently pt_regs on x86_32 has an oddity in that kernel regs
(!user_mode(regs)) are short two entries (esp/ss). This means that any
code trying to use them (typically: regs->sp) needs to jump through
some unfortunate hoops.

Change the entry code to fix this up and create a full pt_regs frame.

This then simplifies various trampolines in ftrace and kprobes, the
stack unwinder, ptrace, kdump and kgdb.

Much thanks to Josh for help with the cleanups!

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2019-05-07 23:25:54 +02:00
committed by Ingo Molnar
parent ea1ed38dba
commit 3c88c692c2
15 changed files with 177 additions and 190 deletions
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29
arch/x86/kernel/ptrace.c
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@@ -154,35 +154,6 @@ static inline bool invalid_selector(u16 value)
#define FLAG_MASK FLAG_MASK_32
/*
* X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
* when it traps. The previous stack will be directly underneath the saved
* registers, and 'sp/ss' won't even have been saved. Thus the '&regs->sp'.
*
* Now, if the stack is empty, '&regs->sp' is out of range. In this
* case we try to take the previous stack. To always return a non-null
* stack pointer we fall back to regs as stack if no previous stack
* exists.
*
* This is valid only for kernel mode traps.
*/
unsigned long kernel_stack_pointer(struct pt_regs *regs)
{
unsigned long context = (unsigned long)regs & ~(THREAD_SIZE - 1);
unsigned long sp = (unsigned long)&regs->sp;
u32 *prev_esp;
if (context == (sp & ~(THREAD_SIZE - 1)))
return sp;
prev_esp = (u32 *)(context);
if (*prev_esp)
return (unsigned long)*prev_esp;
return (unsigned long)regs;
}
EXPORT_SYMBOL_GPL(kernel_stack_pointer);
static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long regno)
{
BUILD_BUG_ON(offsetof(struct pt_regs, bx) != 0);