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arm64: Fix text patching logic when using fixmap

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Patch 2f896d5866 ("arm64: use fixmap for text patching") changed
the way we patch the kernel text, using a fixmap when the kernel or
modules are flagged as read only.

Unfortunately, a flaw in the logic makes it fall over when patching
modules without CONFIG_DEBUG_SET_MODULE_RONX enabled:

[...]
[   32.032636] Call trace:
[   32.032716] [<fffffe00003da0dc>] __copy_to_user+0x2c/0x60
[   32.032837] [<fffffe0000099f08>] __aarch64_insn_write+0x94/0xf8
[   32.033027] [<fffffe000009a0a0>] aarch64_insn_patch_text_nosync+0x18/0x58
[   32.033200] [<fffffe000009c3ec>] ftrace_modify_code+0x58/0x84
[   32.033363] [<fffffe000009c4e4>] ftrace_make_nop+0x3c/0x58
[   32.033532] [<fffffe0000164420>] ftrace_process_locs+0x3d0/0x5c8
[   32.033709] [<fffffe00001661cc>] ftrace_module_init+0x28/0x34
[   32.033882] [<fffffe0000135148>] load_module+0xbb8/0xfc4
[   32.034044] [<fffffe0000135714>] SyS_finit_module+0x94/0xc4
[...]

This is triggered by the use of virt_to_page() on a module address,
which ends to pointing to Nowhereland if you're lucky, or corrupt
your precious data if not.

This patch fixes the logic by mimicking what is done on arm:
- If we're patching a module and CONFIG_DEBUG_SET_MODULE_RONX is set,
  use vmalloc_to_page().
- If we're patching the kernel and CONFIG_DEBUG_RODATA is set,
  use virt_to_page().
- Otherwise, use the provided address, as we can write to it directly.

Tested on 4.0-rc1 as a KVM guest.

Reported-by: Richard W.M. Jones <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Acked-by: Laura Abbott <[email protected]>
Tested-by: Richard W.M. Jones <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
This commit is contained in:
Marc Zyngier 2015-02-24 16:30:21 +00:00 • committed by Catalin Marinas
commit f6242cac10
1 changed files with 3 additions and 1 deletions
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4
arch/arm64/kernel/insn.c
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@ -87,8 +87,10 @@ static void __kprobes *patch_map(void *addr, int fixmap)
if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
page = vmalloc_to_page(addr);
else
else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
page = virt_to_page(addr);
else
return addr;
BUG_ON(!page);
set_fixmap(fixmap, page_to_phys(page));