From 7829fb09a2b4268b30dd9bc782fa5ebee278b137 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 30 Apr 2015 04:13:52 +0200 Subject: [PATCH 1/2] lib: make memzero_explicit more robust against dead store elimination In commit 0b053c951829 ("lib: memzero_explicit: use barrier instead of OPTIMIZER_HIDE_VAR"), we made memzero_explicit() more robust in case LTO would decide to inline memzero_explicit() and eventually find out it could be elimiated as dead store. While using barrier() works well for the case of gcc, recent efforts from LLVMLinux people suggest to use llvm as an alternative to gcc, and there, Stephan found in a simple stand-alone user space example that llvm could nevertheless optimize and thus elimitate the memset(). A similar issue has been observed in the referenced llvm bug report, which is regarded as not-a-bug. Based on some experiments, icc is a bit special on its own, while it doesn't seem to eliminate the memset(), it could do so with an own implementation, and then result in similar findings as with llvm. The fix in this patch now works for all three compilers (also tested with more aggressive optimization levels). Arguably, in the current kernel tree it's more of a theoretical issue, but imho, it's better to be pedantic about it. It's clearly visible with gcc/llvm though, with the below code: if we would have used barrier() only here, llvm would have omitted clearing, not so with barrier_data() variant: static inline void memzero_explicit(void *s, size_t count) { memset(s, 0, count); barrier_data(s); } int main(void) { char buff[20]; memzero_explicit(buff, sizeof(buff)); return 0; } $ gcc -O2 test.c $ gdb a.out (gdb) disassemble main Dump of assembler code for function main: 0x0000000000400400 <+0>: lea -0x28(%rsp),%rax 0x0000000000400405 <+5>: movq $0x0,-0x28(%rsp) 0x000000000040040e <+14>: movq $0x0,-0x20(%rsp) 0x0000000000400417 <+23>: movl $0x0,-0x18(%rsp) 0x000000000040041f <+31>: xor %eax,%eax 0x0000000000400421 <+33>: retq End of assembler dump. $ clang -O2 test.c $ gdb a.out (gdb) disassemble main Dump of assembler code for function main: 0x00000000004004f0 <+0>: xorps %xmm0,%xmm0 0x00000000004004f3 <+3>: movaps %xmm0,-0x18(%rsp) 0x00000000004004f8 <+8>: movl $0x0,-0x8(%rsp) 0x0000000000400500 <+16>: lea -0x18(%rsp),%rax 0x0000000000400505 <+21>: xor %eax,%eax 0x0000000000400507 <+23>: retq End of assembler dump. As gcc, clang, but also icc defines __GNUC__, it's sufficient to define this in compiler-gcc.h only to be picked up. For a fallback or otherwise unsupported compiler, we define it as a barrier. Similarly, for ecc which does not support gcc inline asm. Reference: https://llvm.org/bugs/show_bug.cgi?id=15495 Reported-by: Stephan Mueller Tested-by: Stephan Mueller Signed-off-by: Daniel Borkmann Cc: Theodore Ts'o Cc: Stephan Mueller Cc: Hannes Frederic Sowa Cc: mancha security Cc: Mark Charlebois Cc: Behan Webster Signed-off-by: Herbert Xu --- include/linux/compiler-gcc.h | 16 +++++++++++++++- include/linux/compiler-intel.h | 3 +++ include/linux/compiler.h | 4 ++++ lib/string.c | 2 +- 4 files changed, 23 insertions(+), 2 deletions(-) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index cdf13ca7cac3..371e560d13cf 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -9,10 +9,24 @@ + __GNUC_MINOR__ * 100 \ + __GNUC_PATCHLEVEL__) - /* Optimization barrier */ + /* The "volatile" is due to gcc bugs */ #define barrier() __asm__ __volatile__("": : :"memory") +/* + * This version is i.e. to prevent dead stores elimination on @ptr + * where gcc and llvm may behave differently when otherwise using + * normal barrier(): while gcc behavior gets along with a normal + * barrier(), llvm needs an explicit input variable to be assumed + * clobbered. The issue is as follows: while the inline asm might + * access any memory it wants, the compiler could have fit all of + * @ptr into memory registers instead, and since @ptr never escaped + * from that, it proofed that the inline asm wasn't touching any of + * it. This version works well with both compilers, i.e. we're telling + * the compiler that the inline asm absolutely may see the contents + * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495 + */ +#define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory") /* * This macro obfuscates arithmetic on a variable address so that gcc diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h index ba147a1727e6..0c9a2f2c2802 100644 --- a/include/linux/compiler-intel.h +++ b/include/linux/compiler-intel.h @@ -13,9 +13,12 @@ /* Intel ECC compiler doesn't support gcc specific asm stmts. * It uses intrinsics to do the equivalent things. */ +#undef barrier_data #undef RELOC_HIDE #undef OPTIMIZER_HIDE_VAR +#define barrier_data(ptr) barrier() + #define RELOC_HIDE(ptr, off) \ ({ unsigned long __ptr; \ __ptr = (unsigned long) (ptr); \ diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 0e41ca0e5927..867722591be2 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -169,6 +169,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); # define barrier() __memory_barrier() #endif +#ifndef barrier_data +# define barrier_data(ptr) barrier() +#endif + /* Unreachable code */ #ifndef unreachable # define unreachable() do { } while (1) diff --git a/lib/string.c b/lib/string.c index a5792019193c..bb3d4b6993c4 100644 --- a/lib/string.c +++ b/lib/string.c @@ -607,7 +607,7 @@ EXPORT_SYMBOL(memset); void memzero_explicit(void *s, size_t count) { memset(s, 0, count); - barrier(); + barrier_data(s); } EXPORT_SYMBOL(memzero_explicit); From f440c4ee3e53f767974fe60bcbc0b6687a5fb53f Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=C3=81lvaro=20Fern=C3=A1ndez=20Rojas?= Date: Sat, 2 May 2015 12:08:42 +0200 Subject: [PATCH 2/2] hwrng: bcm63xx - Fix driver compilation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit - s/clk_didsable_unprepare/clk_disable_unprepare - s/prov/priv - s/error/ret (bcm63xx_rng_probe) Fixes: 6229c16060fe ("hwrng: bcm63xx - make use of devm_hwrng_register") Signed-off-by: Álvaro Fernández Rojas Acked-by: Florian Fainelli Signed-off-by: Herbert Xu --- drivers/char/hw_random/bcm63xx-rng.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/drivers/char/hw_random/bcm63xx-rng.c b/drivers/char/hw_random/bcm63xx-rng.c index d1494ecd9e11..4b31f1387f37 100644 --- a/drivers/char/hw_random/bcm63xx-rng.c +++ b/drivers/char/hw_random/bcm63xx-rng.c @@ -57,7 +57,7 @@ static void bcm63xx_rng_cleanup(struct hwrng *rng) val &= ~RNG_EN; __raw_writel(val, priv->regs + RNG_CTRL); - clk_didsable_unprepare(prov->clk); + clk_disable_unprepare(priv->clk); } static int bcm63xx_rng_data_present(struct hwrng *rng, int wait) @@ -97,14 +97,14 @@ static int bcm63xx_rng_probe(struct platform_device *pdev) priv->rng.name = pdev->name; priv->rng.init = bcm63xx_rng_init; priv->rng.cleanup = bcm63xx_rng_cleanup; - prov->rng.data_present = bcm63xx_rng_data_present; + priv->rng.data_present = bcm63xx_rng_data_present; priv->rng.data_read = bcm63xx_rng_data_read; priv->clk = devm_clk_get(&pdev->dev, "ipsec"); if (IS_ERR(priv->clk)) { - error = PTR_ERR(priv->clk); - dev_err(&pdev->dev, "no clock for device: %d\n", error); - return error; + ret = PTR_ERR(priv->clk); + dev_err(&pdev->dev, "no clock for device: %d\n", ret); + return ret; } if (!devm_request_mem_region(&pdev->dev, r->start, @@ -120,11 +120,11 @@ static int bcm63xx_rng_probe(struct platform_device *pdev) return -ENOMEM; } - error = devm_hwrng_register(&pdev->dev, &priv->rng); - if (error) { + ret = devm_hwrng_register(&pdev->dev, &priv->rng); + if (ret) { dev_err(&pdev->dev, "failed to register rng device: %d\n", - error); - return error; + ret); + return ret; } dev_info(&pdev->dev, "registered RNG driver\n");