From: Nick Desaulniers ndesaulniers@google.com
[ Upstream commit 4d45bc82df667ad9e9cb8361830e54fc1264e993 ]
When the following configs are enabled: * CORESIGHT * CORESIGHT_SOURCE_ETM4X * UBSAN * UBSAN_TRAP
Clang fails assemble the kernel with the error: <instantiation>:1:7: error: expected constant expression in '.inst' directive .inst (0xd5200000|((((2) << 19) | ((1) << 16) | (((((((((((0x160 + (i * 4))))) >> 2))) >> 7) & 0x7)) << 12) | ((((((((((0x160 + (i * 4))))) >> 2))) & 0xf)) << 8) | (((((((((((0x160 + (i * 4))))) >> 2))) >> 4) & 0x7)) << 5)))|(.L__reg_num_x8)) ^ drivers/hwtracing/coresight/coresight-etm4x-core.c:702:4: note: while in macro instantiation etm4x_relaxed_read32(csa, TRCCNTVRn(i)); ^ drivers/hwtracing/coresight/coresight-etm4x.h:403:4: note: expanded from macro 'etm4x_relaxed_read32' read_etm4x_sysreg_offset((offset), false))) ^ drivers/hwtracing/coresight/coresight-etm4x.h:383:12: note: expanded from macro 'read_etm4x_sysreg_offset' __val = read_etm4x_sysreg_const_offset((offset)); \ ^ drivers/hwtracing/coresight/coresight-etm4x.h:149:2: note: expanded from macro 'read_etm4x_sysreg_const_offset' READ_ETM4x_REG(ETM4x_OFFSET_TO_REG(offset)) ^ drivers/hwtracing/coresight/coresight-etm4x.h:144:2: note: expanded from macro 'READ_ETM4x_REG' read_sysreg_s(ETM4x_REG_NUM_TO_SYSREG((reg))) ^ arch/arm64/include/asm/sysreg.h:1108:15: note: expanded from macro 'read_sysreg_s' asm volatile(__mrs_s("%0", r) : "=r" (__val)); \ ^ arch/arm64/include/asm/sysreg.h:1074:2: note: expanded from macro '__mrs_s' " mrs_s " v ", " __stringify(r) "\n" \ ^
Consider the definitions of TRCSSCSRn and TRCCNTVRn: drivers/hwtracing/coresight/coresight-etm4x.h:56 #define TRCCNTVRn(n) (0x160 + (n * 4)) drivers/hwtracing/coresight/coresight-etm4x.h:81 #define TRCSSCSRn(n) (0x2A0 + (n * 4))
Where the macro parameter is expanded to i; a loop induction variable from etm4_disable_hw.
When any compiler can determine that loops may be unrolled, then the __builtin_constant_p check in read_etm4x_sysreg_offset() defined in drivers/hwtracing/coresight/coresight-etm4x.h may evaluate to true. This can lead to the expression `(0x160 + (i * 4))` being passed to read_etm4x_sysreg_const_offset. Via the trace above, this is passed through READ_ETM4x_REG, read_sysreg_s, and finally to __mrs_s where it is string-ified and used directly in inline asm.
Regardless of which compiler or compiler options determine whether a loop can or can't be unrolled, which determines whether __builtin_constant_p evaluates to true when passed an expression using a loop induction variable, it is NEVER safe to allow the preprocessor to construct inline asm like: asm volatile (".inst (0x160 + (i * 4))" : "=r"(__val)); ^ expected constant expression
Instead of read_etm4x_sysreg_offset() using __builtin_constant_p(), use __is_constexpr from include/linux/const.h instead to ensure only expressions that are valid integer constant expressions get passed through to read_sysreg_s().
This is not a bug in clang; it's a potentially unsafe use of the macro arguments in read_etm4x_sysreg_offset dependent on __builtin_constant_p.
Link: https://github.com/ClangBuiltLinux/linux/issues/1310 Reported-by: Arnd Bergmann arnd@kernel.org Reported-by: Tao Zhang quic_taozha@quicinc.com Signed-off-by: Nick Desaulniers ndesaulniers@google.com Acked-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Suzuki K Poulose suzuki.poulose@arm.com Link: https://lore.kernel.org/r/20220708231520.3958391-1-ndesaulniers@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hwtracing/coresight/coresight-etm4x.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h index 3c4d69b096ca..dcd52a64fc21 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x.h +++ b/drivers/hwtracing/coresight/coresight-etm4x.h @@ -7,6 +7,7 @@ #define _CORESIGHT_CORESIGHT_ETM_H
#include <asm/local.h> +#include <linux/const.h> #include <linux/spinlock.h> #include <linux/types.h> #include "coresight-priv.h" @@ -417,7 +418,7 @@ ({ \ u64 __val; \ \ - if (__builtin_constant_p((offset))) \ + if (__is_constexpr((offset))) \ __val = read_etm4x_sysreg_const_offset((offset)); \ else \ __val = etm4x_sysreg_read((offset), true, (_64bit)); \