Eric Lee / smarc-ti-linux-kernel

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Commit d4c5efdb97773f59a2b711754ca0953f24516739

Authored by Daniel Borkmann
Committed by Theodore Ts'o
1 parent 7d1311b93e
Exists in ti-lsk-linux-4.1.y and in 10 other branches dlt-processor-sdk-linux-03.00.00.04, processor-sdk-linux-02.00.01, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04

random: add and use memzero_explicit() for clearing data 

zatimend has reported that in his environment (3.16/gcc4.8.3/corei7)
memset() calls which clear out sensitive data in extract_{buf,entropy,
entropy_user}() in random driver are being optimized away by gcc.

Add a helper memzero_explicit() (similarly as explicit_bzero() variants)
that can be used in such cases where a variable with sensitive data is
being cleared out in the end. Other use cases might also be in crypto
code. [ I have put this into lib/string.c though, as it's always built-in
and doesn't need any dependencies then. ]

Fixes kernel bugzilla: 82041

Reported-by: zatimend@hotmail.co.uk
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

Showing 3 changed files with 23 additions and 6 deletions Side-by-side Diff

drivers/char/random.c
Diff comments   View file @ d4c5efd
... ... @@ -1106,7 +1106,7 @@
1106 1106 __mix_pool_bytes(r, hash.w, sizeof(hash.w));
1107 1107 spin_unlock_irqrestore(&r->lock, flags);
1108 1108  
1109   - memset(workspace, 0, sizeof(workspace));
  1109 + memzero_explicit(workspace, sizeof(workspace));
1110 1110  
1111 1111 /*
1112 1112 * In case the hash function has some recognizable output
... ... @@ -1118,7 +1118,7 @@
1118 1118 hash.w[2] ^= rol32(hash.w[2], 16);
1119 1119  
1120 1120 memcpy(out, &hash, EXTRACT_SIZE);
1121   - memset(&hash, 0, sizeof(hash));
  1121 + memzero_explicit(&hash, sizeof(hash));
1122 1122 }
1123 1123  
1124 1124 /*
... ... @@ -1175,7 +1175,7 @@
1175 1175 }
1176 1176  
1177 1177 /* Wipe data just returned from memory */
1178   - memset(tmp, 0, sizeof(tmp));
  1178 + memzero_explicit(tmp, sizeof(tmp));
1179 1179  
1180 1180 return ret;
1181 1181 }
... ... @@ -1218,7 +1218,7 @@
1218 1218 }
1219 1219  
1220 1220 /* Wipe data just returned from memory */
1221   - memset(tmp, 0, sizeof(tmp));
  1221 + memzero_explicit(tmp, sizeof(tmp));
1222 1222  
1223 1223 return ret;
1224 1224 }
include/linux/string.h
Diff comments   View file @ d4c5efd
... ... @@ -132,7 +132,7 @@
132 132 #endif
133 133  
134 134 extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
135   - const void *from, size_t available);
  135 + const void *from, size_t available);
136 136  
137 137 /**
138 138 * strstarts - does @str start with @prefix?
... ... @@ -144,7 +144,8 @@
144 144 return strncmp(str, prefix, strlen(prefix)) == 0;
145 145 }
146 146  
147   -extern size_t memweight(const void *ptr, size_t bytes);
  147 +size_t memweight(const void *ptr, size_t bytes);
  148 +void memzero_explicit(void *s, size_t count);
148 149  
149 150 /**
150 151 * kbasename - return the last part of a pathname.
... ... @@ -604,6 +604,22 @@
604 604 EXPORT_SYMBOL(memset);
605 605 #endif
606 606  
  607 +/**
  608 + * memzero_explicit - Fill a region of memory (e.g. sensitive
  609 + * keying data) with 0s.
  610 + * @s: Pointer to the start of the area.
  611 + * @count: The size of the area.
  612 + *
  613 + * memzero_explicit() doesn't need an arch-specific version as
  614 + * it just invokes the one of memset() implicitly.
  615 + */
  616 +void memzero_explicit(void *s, size_t count)
  617 +{
  618 + memset(s, 0, count);
  619 + OPTIMIZER_HIDE_VAR(s);
  620 +}
  621 +EXPORT_SYMBOL(memzero_explicit);
  622 +
607 623 #ifndef __HAVE_ARCH_MEMCPY
608 624 /**
609 625 * memcpy - Copy one area of memory to another