2021-06-25 17:45:15 -07:00
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string: Introduce strtomem() and strtomem_pad()
One of the "legitimate" uses of strncpy() is copying a NUL-terminated
string into a fixed-size non-NUL-terminated character array. To avoid
the weaknesses and ambiguity of intent when using strncpy(), provide
replacement functions that explicitly distinguish between trailing
padding and not, and require the destination buffer size be discoverable
by the compiler.
For example:
struct obj {
int foo;
char small[4] __nonstring;
char big[8] __nonstring;
int bar;
};
struct obj p;
/* This will truncate to 4 chars with no trailing NUL */
strncpy(p.small, "hello", sizeof(p.small));
/* p.small contains 'h', 'e', 'l', 'l' */
/* This will NUL pad to 8 chars. */
strncpy(p.big, "hello", sizeof(p.big));
/* p.big contains 'h', 'e', 'l', 'l', 'o', '\0', '\0', '\0' */
When the "__nonstring" attributes are missing, the intent of the
programmer becomes ambiguous for whether the lack of a trailing NUL
in the p.small copy is a bug. Additionally, it's not clear whether
the trailing padding in the p.big copy is _needed_. Both cases
become unambiguous with:
strtomem(p.small, "hello");
strtomem_pad(p.big, "hello", 0);
See also https://github.com/KSPP/linux/issues/90
Expand the memcpy KUnit tests to include these functions.
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
2022-08-26 11:04:43 -07:00
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2021-06-25 17:45:15 -07:00
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2024-02-21 17:27:16 +08:00
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2021-06-25 17:45:15 -07:00
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string: Introduce strtomem() and strtomem_pad()
One of the "legitimate" uses of strncpy() is copying a NUL-terminated
string into a fixed-size non-NUL-terminated character array. To avoid
the weaknesses and ambiguity of intent when using strncpy(), provide
replacement functions that explicitly distinguish between trailing
padding and not, and require the destination buffer size be discoverable
by the compiler.
For example:
struct obj {
int foo;
char small[4] __nonstring;
char big[8] __nonstring;
int bar;
};
struct obj p;
/* This will truncate to 4 chars with no trailing NUL */
strncpy(p.small, "hello", sizeof(p.small));
/* p.small contains 'h', 'e', 'l', 'l' */
/* This will NUL pad to 8 chars. */
strncpy(p.big, "hello", sizeof(p.big));
/* p.big contains 'h', 'e', 'l', 'l', 'o', '\0', '\0', '\0' */
When the "__nonstring" attributes are missing, the intent of the
programmer becomes ambiguous for whether the lack of a trailing NUL
in the p.small copy is a bug. Additionally, it's not clear whether
the trailing padding in the p.big copy is _needed_. Both cases
become unambiguous with:
strtomem(p.small, "hello");
strtomem_pad(p.big, "hello", 0);
See also https://github.com/KSPP/linux/issues/90
Expand the memcpy KUnit tests to include these functions.
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
2022-08-26 11:04:43 -07:00
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2021-06-25 17:45:15 -07:00
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2024-02-21 17:27:16 +08:00
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2021-06-25 17:45:15 -07:00
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x86/mem: Move memmove to out of line assembler
When building ARCH=i386 with CONFIG_LTO_CLANG_FULL=y, it's possible
(depending on additional configs which I have not been able to isolate)
to observe a failure during register allocation:
error: inline assembly requires more registers than available
when memmove is inlined into tcp_v4_fill_cb() or tcp_v6_fill_cb().
memmove is quite large and probably shouldn't be inlined due to size
alone. A noinline function attribute would be the simplest fix, but
there's a few things that stand out with the current definition:
In addition to having complex constraints that can't always be resolved,
the clobber list seems to be missing %bx. By using numbered operands
rather than symbolic operands, the constraints are quite obnoxious to
refactor.
Having a large function be 99% inline asm is a code smell that this
function should simply be written in stand-alone out-of-line assembler.
Moving this to out of line assembler guarantees that the
compiler cannot inline calls to memmove.
This has been done previously for 64b:
commit 9599ec0471de ("x86-64, mem: Convert memmove() to assembly file
and fix return value bug")
That gives the opportunity for other cleanups like fixing the
inconsistent use of tabs vs spaces and instruction suffixes, and the
label 3 appearing twice. Symbolic operands, local labels, and
additional comments would provide this code with a fresh coat of paint.
Finally, add a test that tickles the `rep movsl` implementation to test
it for correctness, since it has implicit operands.
Suggested-by: Ingo Molnar <mingo@kernel.org>
Suggested-by: David Laight <David.Laight@aculab.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/all/20221018172155.287409-1-ndesaulniers%40google.com
2022-10-18 10:21:55 -07:00
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2021-06-25 17:45:15 -07:00
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x86/mem: Move memmove to out of line assembler
When building ARCH=i386 with CONFIG_LTO_CLANG_FULL=y, it's possible
(depending on additional configs which I have not been able to isolate)
to observe a failure during register allocation:
error: inline assembly requires more registers than available
when memmove is inlined into tcp_v4_fill_cb() or tcp_v6_fill_cb().
memmove is quite large and probably shouldn't be inlined due to size
alone. A noinline function attribute would be the simplest fix, but
there's a few things that stand out with the current definition:
In addition to having complex constraints that can't always be resolved,
the clobber list seems to be missing %bx. By using numbered operands
rather than symbolic operands, the constraints are quite obnoxious to
refactor.
Having a large function be 99% inline asm is a code smell that this
function should simply be written in stand-alone out-of-line assembler.
Moving this to out of line assembler guarantees that the
compiler cannot inline calls to memmove.
This has been done previously for 64b:
commit 9599ec0471de ("x86-64, mem: Convert memmove() to assembly file
and fix return value bug")
That gives the opportunity for other cleanups like fixing the
inconsistent use of tabs vs spaces and instruction suffixes, and the
label 3 appearing twice. Symbolic operands, local labels, and
additional comments would provide this code with a fresh coat of paint.
Finally, add a test that tickles the `rep movsl` implementation to test
it for correctness, since it has implicit operands.
Suggested-by: Ingo Molnar <mingo@kernel.org>
Suggested-by: David Laight <David.Laight@aculab.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/all/20221018172155.287409-1-ndesaulniers%40google.com
2022-10-18 10:21:55 -07:00
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2021-06-25 17:45:15 -07:00
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2021-05-17 20:16:57 -07:00
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2021-05-17 20:16:57 -07:00
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2021-06-25 17:45:15 -07:00
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2021-05-17 20:16:57 -07:00
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2021-05-17 20:16:57 -07:00
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2021-06-25 17:45:15 -07:00
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2022-09-28 14:17:05 -07:00
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2021-06-25 17:45:15 -07:00
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2023-07-25 21:25:17 +00:00
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2021-06-25 17:45:15 -07:00
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2024-05-31 15:45:22 -07:00
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2021-06-25 17:45:15 -07:00
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