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x86,rethook: Fix arch_rethook_trampoline() to generate a complete pt_regs

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Currently arch_rethook_trampoline() generates an almost complete
pt_regs on-stack, everything except regs->ss that is, that currently
points to the fake return address, which is not a valid segment
descriptor.

Since interpretation of regs->[sb]p should be done in the context of
regs->ss, and we have code actually doing that (see
arch/x86/lib/insn-eval.c for instance), complete the job by also
pushing ss.

This ensures that anybody who does do look at regs->ss doesn't
mysteriously malfunction, avoiding much future pain.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/bpf/164826164851.2455864.17272661073069737350.stgit@devnote2
This commit is contained in:
Peter Zijlstra 2022-03-26 11:27:28 +09:00 committed by Alexei Starovoitov
parent f3a112c0c4
commit 0ef6f5c093
1 changed files with 13 additions and 11 deletions
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24
arch/x86/kernel/rethook.c
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@ -29,29 +29,31 @@ asm(
/* Push a fake return address to tell the unwinder it's a rethook. */
" pushq $arch_rethook_trampoline\n"
UNWIND_HINT_FUNC
/* Save the 'sp - 8', this will be fixed later. */
" pushq $" __stringify(__KERNEL_DS) "\n"
/* Save the 'sp - 16', this will be fixed later. */
" pushq %rsp\n"
" pushfq\n"
SAVE_REGS_STRING
" movq %rsp, %rdi\n"
" call arch_rethook_trampoline_callback\n"
RESTORE_REGS_STRING
/* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
" addq $8, %rsp\n"
/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
" addq $16, %rsp\n"
" popfq\n"
#else
/* Push a fake return address to tell the unwinder it's a rethook. */
" pushl $arch_rethook_trampoline\n"
UNWIND_HINT_FUNC
/* Save the 'sp - 4', this will be fixed later. */
" pushl %ss\n"
/* Save the 'sp - 8', this will be fixed later. */
" pushl %esp\n"
" pushfl\n"
SAVE_REGS_STRING
" movl %esp, %eax\n"
" call arch_rethook_trampoline_callback\n"
RESTORE_REGS_STRING
/* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
" addl $4, %esp\n"
/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
" addl $8, %esp\n"
" popfl\n"
#endif
ASM_RET
@ -73,8 +75,8 @@ __used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
#endif
regs->ip = (unsigned long)&arch_rethook_trampoline;
regs->orig_ax = ~0UL;
regs->sp += sizeof(long);
frame_pointer = &regs->sp + 1;
regs->sp += 2*sizeof(long);
frame_pointer = (long *)(regs + 1);
/*
* The return address at 'frame_pointer' is recovered by the
@ -84,10 +86,10 @@ __used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
/*
* Copy FLAGS to 'pt_regs::sp' so that arch_rethook_trapmoline()
* Copy FLAGS to 'pt_regs::ss' so that arch_rethook_trapmoline()
* can do RET right after POPF.
*/
regs->sp = regs->flags;
*(unsigned long *)&regs->ss = regs->flags;
}
NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
@ -105,7 +107,7 @@ STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
void arch_rethook_fixup_return(struct pt_regs *regs,
unsigned long correct_ret_addr)
{
unsigned long *frame_pointer = &regs->sp + 1;
unsigned long *frame_pointer = (void *)(regs + 1);
/* Replace fake return address with real one. */
*frame_pointer = correct_ret_addr;