kernel/sys.c: fix potential Spectre v1 issue
`resource' can be controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability. This issue was detected with the help of Smatch: kernel/sys.c:1474 __do_compat_sys_old_getrlimit() warn: potential spectre issue 'get_current()->signal->rlim' (local cap) kernel/sys.c:1455 __do_sys_old_getrlimit() warn: potential spectre issue 'get_current()->signal->rlim' (local cap) Fix this by sanitizing *resource* before using it to index current->signal->rlim Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1]. [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2 Link: http://lkml.kernel.org/r/20180515030038.GA11822@embeddedor.com Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -71,6 +71,9 @@
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#include <asm/io.h>
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#include <asm/unistd.h>
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/* Hardening for Spectre-v1 */
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#include <linux/nospec.h>
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#include "uid16.h"
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#ifndef SET_UNALIGN_CTL
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@ -1453,6 +1456,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
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if (resource >= RLIM_NLIMITS)
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return -EINVAL;
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resource = array_index_nospec(resource, RLIM_NLIMITS);
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task_lock(current->group_leader);
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x = current->signal->rlim[resource];
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task_unlock(current->group_leader);
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@ -1472,6 +1476,7 @@ COMPAT_SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
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if (resource >= RLIM_NLIMITS)
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return -EINVAL;
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resource = array_index_nospec(resource, RLIM_NLIMITS);
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task_lock(current->group_leader);
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r = current->signal->rlim[resource];
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task_unlock(current->group_leader);
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