| Message ID | CACXcFm=kwziZ5Etdevu0uq_t5qy0NbGY753WfLvnwkMqtU9Tvg@mail.gmail.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | memset() in crypto code | expand |
On Tue, Nov 16, 2021 at 07:25:22PM +0800, Sandy Harris wrote: > Replace memset(address,0,bytes) which may be optimised away > with memzero_explicit(address,bytes) which resists > such optimisation > > --- > crypto/des_generic.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/crypto/des_generic.c b/crypto/des_generic.c > index c85354a5e94c..105a32e7afea 100644 > --- a/crypto/des_generic.c > +++ b/crypto/des_generic.c > @@ -30,7 +30,7 @@ static int des_setkey(struct crypto_tfm *tfm, const u8 *key, > err = 0; > } > if (err) > - memset(dctx, 0, sizeof(*dctx)); > + memzero_explicit(dctx, sizeof(*dctx)); > return err; > } > > @@ -62,7 +62,7 @@ static int des3_ede_setkey(struct crypto_tfm *tfm, > const u8 *key, > err = 0; > } > if (err) > - memset(dctx, 0, sizeof(*dctx)); > + memzero_explicit(dctx, sizeof(*dctx)); > return err; > } > > -- Hi, This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him a patch that has triggered this response. He used to manually respond to these common problems, but in order to save his sanity (he kept writing the same thing over and over, yet to different people), I was created. Hopefully you will not take offence and will fix the problem in your patch and resubmit it so that it can be accepted into the Linux kernel tree. You are receiving this message because of the following common error(s) as indicated below: - Your patch does not have a Signed-off-by: line. Please read the kernel file, Documentation/SubmittingPatches and resend it after adding that line. Note, the line needs to be in the body of the email, before the patch, not at the bottom of the patch or in the email signature. - You did not write a descriptive Subject: for the patch, allowing Greg, and everyone else, to know what this patch is all about. Please read the section entitled "The canonical patch format" in the kernel file, Documentation/SubmittingPatches for what a proper Subject: line should look like. If you wish to discuss this problem further, or you have questions about how to resolve this issue, please feel free to respond to this email and Greg will reply once he has dug out from the pending patches received from other developers. thanks, greg k-h's patch email bot
On Tue, Nov 16, 2021 at 07:25:22PM +0800, Sandy Harris wrote: > Replace memset(address,0,bytes) which may be optimised away > with memzero_explicit(address,bytes) which resists > such optimisation > > --- > crypto/des_generic.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/crypto/des_generic.c b/crypto/des_generic.c > index c85354a5e94c..105a32e7afea 100644 > --- a/crypto/des_generic.c > +++ b/crypto/des_generic.c > @@ -30,7 +30,7 @@ static int des_setkey(struct crypto_tfm *tfm, const u8 *key, > err = 0; > } > if (err) > - memset(dctx, 0, sizeof(*dctx)); > + memzero_explicit(dctx, sizeof(*dctx)); > return err; > } > > @@ -62,7 +62,7 @@ static int des3_ede_setkey(struct crypto_tfm *tfm, > const u8 *key, > err = 0; > } > if (err) > - memset(dctx, 0, sizeof(*dctx)); > + memzero_explicit(dctx, sizeof(*dctx)); > return err; > } > Have you looked at the output of the compiler to see if this really is needed or not? And what exactly are you zeroing out that could be read afterward somehow? thanks, greg k-h
On Tue, Nov 16, 2021 at 12:50:58PM +0100, Greg Kroah-Hartman wrote: > On Tue, Nov 16, 2021 at 07:25:22PM +0800, Sandy Harris wrote: > > Replace memset(address,0,bytes) which may be optimised away > > with memzero_explicit(address,bytes) which resists > > such optimisation > > > > --- > > crypto/des_generic.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/crypto/des_generic.c b/crypto/des_generic.c > > index c85354a5e94c..105a32e7afea 100644 > > --- a/crypto/des_generic.c > > +++ b/crypto/des_generic.c > > @@ -30,7 +30,7 @@ static int des_setkey(struct crypto_tfm *tfm, const u8 *key, > > err = 0; > > } > > if (err) > > - memset(dctx, 0, sizeof(*dctx)); > > + memzero_explicit(dctx, sizeof(*dctx)); > > return err; > > } > > > > @@ -62,7 +62,7 @@ static int des3_ede_setkey(struct crypto_tfm *tfm, > > const u8 *key, > > err = 0; > > } > > if (err) > > - memset(dctx, 0, sizeof(*dctx)); > > + memzero_explicit(dctx, sizeof(*dctx)); > > return err; > > } > > > > Have you looked at the output of the compiler to see if this really is > needed or not? Oh wait, that's not a stack variable, how would this be optimized away at all? If it is, that's a HUGE compiler bug. Is that really happening here? thanks, greg k-h
On Tue, Nov 16, 2021 at 7:51 PM Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > Have you looked at the output of the compiler to see if this really is > needed or not? No. To do that right you'd need to look at (at least) gcc & clang, multiple architectures (cross-compiled & native) & various levels of optimisation. I just looked at the C code. > And what exactly are you zeroing out that could be read afterward > somehow? Whatever it is, the person who wrote the code thought it was worth zeroing out with memset(). The only question is whether it is safer to use memzero_explicit(). Granted in many cases this will not matter unless the kernel is compiled at some optimisation level that does cross-function analysis so it might be "smart" enough to optimise out the memset(). Also granted it does not matter unless an attacker can look inside the running kernel & if he or she has that level of privilege, then you have much else to worry about. Still, it seemed safer to me to use memzero_explicit() in these cases.
On Wed, Nov 17, 2021 at 11:08:45AM +0800, Sandy Harris wrote: > On Tue, Nov 16, 2021 at 7:51 PM Greg Kroah-Hartman > <gregkh@linuxfoundation.org> wrote: > > > Have you looked at the output of the compiler to see if this really is > > needed or not? > > No. To do that right you'd need to look at (at least) gcc & clang, > multiple architectures (cross-compiled & native) & various levels > of optimisation. I just looked at the C code. You should at least look, right? > > And what exactly are you zeroing out that could be read afterward > > somehow? > > Whatever it is, the person who wrote the code thought it was > worth zeroing out with memset(). The only question is whether > it is safer to use memzero_explicit(). > > Granted in many cases this will not matter unless the kernel > is compiled at some optimisation level that does cross-function > analysis so it might be "smart" enough to optimise out the > memset(). Also granted it does not matter unless an attacker > can look inside the running kernel & if he or she has that > level of privilege, then you have much else to worry about. As Ard said, there should not be any such "optimization" as this is not something that any non-broken compiler should do. > Still, it seemed safer to me to use memzero_explicit() in > these cases. I do not see why these cases are any different than any other call to memset() is, because this data is not on the stack so nothing should be removed by the compiler, right? thanks, greg k-h
diff --git a/crypto/des_generic.c b/crypto/des_generic.c index c85354a5e94c..105a32e7afea 100644 --- a/crypto/des_generic.c +++ b/crypto/des_generic.c @@ -30,7 +30,7 @@ static int des_setkey(struct crypto_tfm *tfm, const u8 *key, err = 0; } if (err) - memset(dctx, 0, sizeof(*dctx)); + memzero_explicit(dctx, sizeof(*dctx)); return err; } @@ -62,7 +62,7 @@ static int des3_ede_setkey(struct crypto_tfm *tfm, const u8 *key, err = 0; } if (err) - memset(dctx, 0, sizeof(*dctx)); + memzero_explicit(dctx, sizeof(*dctx)); return err; }