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ARM: ensure the signal page contains defined contents

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Ensure that the signal page contains our poison instruction to increase
the protection against ROP attacks and also contains well defined
contents.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Russell King 2021-01-29 10:19:07 +00:00
parent 538eea5362
commit 9c698bff66
1 changed files with 8 additions and 6 deletions
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14
arch/arm/kernel/signal.c
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@ -693,18 +693,20 @@ struct page *get_signal_page(void)
addr = page_address(page);
/* Poison the entire page */
memset32(addr, __opcode_to_mem_arm(0xe7fddef1),
PAGE_SIZE / sizeof(u32));
/* Give the signal return code some randomness */
offset = 0x200 + (get_random_int() & 0x7fc);
signal_return_offset = offset;
/*
* Copy signal return handlers into the vector page, and
* set sigreturn to be a pointer to these.
*/
/* Copy signal return handlers into the page */
memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
ptr = (unsigned long)addr + offset;
flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
/* Flush out all instructions in this page */
ptr = (unsigned long)addr;
flush_icache_range(ptr, ptr + PAGE_SIZE);
return page;
}