From cae2a173fe94ab3a437416af6f092fae2e65837e Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 6 Apr 2015 10:26:17 -0700 Subject: [PATCH] x86: clean up/fix 'copy_in_user()' tail zeroing The rule for 'copy_from_user()' is that it zeroes the remaining kernel buffer even when the copy fails halfway, just to make sure that we don't leave uninitialized kernel memory around. Because even if we check for errors, some kernel buffers stay around after thge copy (think page cache). However, the x86-64 logic for user copies uses a copy_user_generic() function for all the cases, that set the "zerorest" flag for any fault on the source buffer. Which meant that it didn't just try to clear the kernel buffer after a failure in copy_from_user(), it also tried to clear the destination user buffer for the "copy_in_user()" case. Not only is that pointless, it also means that the clearing code has to worry about the tail clearing taking page faults for the user buffer case. Which is just stupid, since that case shouldn't happen in the first place. Get rid of the whole "zerorest" thing entirely, and instead just check if the destination is in kernel space or not. And then just use memset() to clear the tail of the kernel buffer if necessary. Signed-off-by: Linus Torvalds --- arch/x86/include/asm/uaccess_64.h | 2 +- arch/x86/lib/usercopy_64.c | 15 +++++++-------- 2 files changed, 8 insertions(+), 9 deletions(-) diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h index 12a26b979bf1..f2f9b39b274a 100644 --- a/arch/x86/include/asm/uaccess_64.h +++ b/arch/x86/include/asm/uaccess_64.h @@ -231,6 +231,6 @@ __copy_from_user_inatomic_nocache(void *dst, const void __user *src, } unsigned long -copy_user_handle_tail(char *to, char *from, unsigned len, unsigned zerorest); +copy_user_handle_tail(char *to, char *from, unsigned len); #endif /* _ASM_X86_UACCESS_64_H */ diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c index c905e89e19fe..1f33b3d1fd68 100644 --- a/arch/x86/lib/usercopy_64.c +++ b/arch/x86/lib/usercopy_64.c @@ -69,21 +69,20 @@ EXPORT_SYMBOL(copy_in_user); * it is not necessary to optimize tail handling. */ __visible unsigned long -copy_user_handle_tail(char *to, char *from, unsigned len, unsigned zerorest) +copy_user_handle_tail(char *to, char *from, unsigned len) { - char c; - unsigned zero_len; - for (; len; --len, to++) { + char c; + if (__get_user_nocheck(c, from++, sizeof(char))) break; if (__put_user_nocheck(c, to, sizeof(char))) break; } - - for (c = 0, zero_len = len; zerorest && zero_len; --zero_len) - if (__put_user_nocheck(c, to++, sizeof(char))) - break; clac(); + + /* If the destination is a kernel buffer, we always clear the end */ + if ((unsigned long)to >= TASK_SIZE_MAX) + memset(to, 0, len); return len; } -- 2.20.1